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Consolidate reachability logic #10

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derrickstolee
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@derrickstolee derrickstolee commented Jul 13, 2018

There are many places in Git that use a commit walk to determine
reachability between commits and/or refs. A lot of this logic is
duplicated.

I wanted to achieve the following:

  1. Consolidate several different commit walks into one file
  2. Reduce duplicate reachability logic
  3. Increase testability (correctness and performance)
  4. Improve performance of reachability queries

My approach is mostly in three parts:

I. Move code to a new commit-reach.c file.
II. Add a 'test-tool reach' command to test these methods directly.
III. Modify the logic by improving performance and calling methods with
similar logic but different prototypes.

The 'test-tool reach' command is helpful to make sure I don't break
anything as I change the logic, but also so I can test methods that are
normally only exposed by other more complicated commands. For instance,
ref_newer() is part of 'git push -f' and ok_to_give_up() is buried deep
within fetch negotiation. Both of these methods have some problematic
performance issues that are corrected by this series. As I discovered
them, it was clear that it would be better to consolidate walk logic
instead of discovering a new walk in another file hidden somewhere.

For the ok_to_give_up() method, I refactored the method so I could pull
the logic out of the depths of fetch negotiation. In the commit
"commit-reach: make can_all_from_reach... linear" I discuss how the
existing algorithm is quadratic and how we can make it linear. Also, we
can use heuristic knowledge about the shape of the commit graph and the
usual haves/wants to get some extra performance bonus. (The heuristic is
to do a DFS with first-parents first, and stop on first found result. We
expect haves/wants to include ref tips, which typically have their
previous values in their first-parent history.)

One major difference in this series versus the RFC is that I added a new
method 'generation_numbers_enabled()' to detect if we have a commit-graph
file with non-zero generation numbers. Using can_all_from_reach in
is_descendant_of is only faster if we have generation numbers as a cutoff.

V2 Update: The biggest material change in this version is that we drop the
method declarations from commit.h, which requires adding a lot of references
to commit-reach.h across the codebase. This change is in a commit on its own.
In addition, we have the following style-based cleanups:

  • Use 'unsigned int' for the flag variables.

  • Properly align the here-doc test input data.

  • Use singe rev-parse commands in test output, and pipe the OIDs through 'sort'

  • Check output of parse_commit()

  • Update flag documentation in object.h

  • Add tests for commit_contains() including both algorithms.

  • Reduce size of "mixed-mode" commit-graph to ensure we start commit walks
    'above' the graph and then walk into the commits with generation numbers.

Thanks,
-Stolee

This series is based on jt/commit-graph-per-object-store

Cc: sbeller@google.com
Cc: jonathantanmy@google.com

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An error occurred while submitting:

Error: git format-patch --thread --stdout --signature=gitgitgadget --add-header=Fcc: Sent --add-header=Content-Type: text/plain; charset=UTF-8 --add-header=Content-Transfer-Encoding: 8bit --add-header=MIME-Version: 1.0 --base upstream/master --to=git@vger.kernel.org --cc=Junio C Hamano gitster@pobox.com --cover-letter upstream/master..a60b701 failed: 128,
fatal: base commit should be the ancestor of revision list

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An error occurred while submitting:

Error: git format-patch --thread --stdout --signature=gitgitgadget --add-header=Fcc: Sent --add-header=Content-Type: text/plain; charset=UTF-8 --add-header=Content-Transfer-Encoding: 8bit --add-header=MIME-Version: 1.0 --base 9026cfc --to=git@vger.kernel.org --cc=Junio C Hamano gitster@pobox.com --cover-letter 9026cfc..a60b701 failed: 128,
fatal: base commit should be the ancestor of revision list

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gitgitgadget bot commented Jul 16, 2018

Submitted as pull.10.git.gitgitgadget@gmail.com

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dscho commented Jul 16, 2018

So the build & test failed... but it is in the submodule code!

clicketyclick

Ah! You target pu, which is currently broken: https://git-for-windows.visualstudio.com/git/git%20Team/_build/results?buildId=12365&view=logs (same issue, so it is not your patch series' fault).

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dscho commented Jul 19, 2018

@derrickstolee Maybe we need to mirror the branches from https://github.com/gitster/git here, so that you can target the correct branch in pu? It just causes too much pain, obviously, to base your branch on top of pu.

Of course, you could also rebase your branch on top of the respective branch instead of pu...

There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.

The method declarations in commit.h are not touched by this commit and
will be moved in a following commit. Many consumers need to point to
commit-reach.h and that would bloat this commit.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
These methods are now declared in commit-reach.h. Remove them from
commit.h and add new include statements in all files that require these
declarations.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.

The ref_newer() method is used by 'git push -f' to check if a force-push
is necessary. By making the method public, we make it possible to test
the method directly without setting up an envieronment where a 'git
push' call makes sense.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.

All methods are direct moves, except we also make the commit_contains()
method public so its consumers in ref-filter.c can still call it. We can
also test this method in a test-tool in a later commit.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
In anticipation of moving the reachable() method to commit-reach.c,
modify the prototype to be more generic to flags known outside of
upload-pack.c. Also rename 'want' to 'from' to make the statement
more clear outside of the context of haves/wants negotiation.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
In anticipation of consolidating all commit reachability algorithms,
refactor ok_to_give_up() in order to allow splitting its logic into
an external method.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
The ok_to_give_up() method uses the commit date as a cutoff to avoid
walking the entire reachble set of commits. Before moving the
reachable() method to commit-reach.c, pull out the dependence on the
global constant 'oldest_have' with a 'min_commit_date' parameter.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.

The can_all_from_reach_with_flags method is used in a stateful way by
upload-pack.c. The parameters are very flexible, so we will be able to
use its commit walking logic for many other callers.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
As we prepare to change the behavior of the algorithms in
commit-reach.c, create a new test-tool subcommand 'reach' to test these
methods on interesting commit-graph shapes.

To use the new test-tool, use 'test-tool reach <method>' and provide
input to stdin that describes the inputs to the method. Currently, we
only implement the ref_newer method, which requires two commits. Use
lines "A:<committish>" and "B:<committish>" for the two inputs. We will
expand this input later to accommodate methods that take lists of
commits.

The test t6600-test-reach.sh creates a repo whose commits form a
two-dimensional grid. This grid makes it easy for us to determine
reachability because commit-A-B can reach commit-X-Y if and only if A is
at least X and B is at least Y. This helps create interesting test cases
for each result of the methods in commit-reach.c.

We test all methods in three different states of the commit-graph file:
Non-existent (no generation numbers), fully computed, and mixed (some
commits have generation numbers and others do not).

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
The is_descendant_of method takes a single commit as its first parameter
and a list of commits as its second parameter. Extend the input of the
'test-tool reach' command to take multiple lines of the form
"X:<committish>" to construct a list of commits. Pass these to
is_descendant_of and create tests that check each result.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
The get_merge_bases_many method returns a list of merge bases for a
single commit (A) against a list of commits (X). Some care is needed in
constructing the expected behavior because the result is not the
expected merge-base for an octopus merge with those parents but instead
the set of maximal commits that are reachable from A and at least one of
the commits in X.

Add get_merge_bases_many to 'test-tool reach' and create a test that
demonstrates that this output returns multiple results. Specifically, we
select a list of three commits such that we output two commits that are
reachable from one of the first two, respectively, and none are
reachable from the third.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
The can_all_from_reach_with_flags method is used by ok_to_give_up in
upload-pack.c to see if we have done enough negotiation during a fetch.
This method is intentionally created to preserve state between calls to
assist with stateful negotiation, such as over SSH.

To make this method testable, add a new can_all_from_reach method that
does the initial setup and final tear-down. We will later use this
method in production code. Call the method from 'test-tool reach' for
now.

Since this is a many-to-many reachability query, add a new type of input
to the 'test-tool reach' input format. Lines "Y:<committish>" create a
list of commits to be the reachability targets from the commits in the
'X' list. In the context of fetch negotiation, the 'X' commits are the
'want' commits and the 'Y' commits are the 'have' commits.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
dscho pushed a commit that referenced this pull request Oct 31, 2022
dscho pushed a commit that referenced this pull request Oct 31, 2022
dscho pushed a commit that referenced this pull request Nov 8, 2022
When "read_strategy_opts()" is called we may have populated the
"opts->strategy" before, so we'll need to free() it to avoid leaking
memory.

We populate it before because we cal get_replay_opts() from within
"rebase.c" with an already populated "opts", which we then copy. Then
if we're doing a "rebase -i" the sequencer API itself will promptly
clobber our alloc'd version of it with its own.

If this code is changed to do, instead of the added free() here a:

	if (opts->strategy)
		opts->strategy = xstrdup("another leak");

We get a couple of stacktraces from -fsanitize=leak showing how we
ended up clobbering the already allocated value, i.e.:

	Direct leak of 6 byte(s) in 1 object(s) allocated from:
	    #0 0x7f2e8cd45545 in __interceptor_malloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:75
	    #1 0x7f2e8cb0fcaa in __GI___strdup string/strdup.c:42
	    #2 0x6c4778 in xstrdup wrapper.c:39
	    #3 0x66bcb8 in read_strategy_opts sequencer.c:2902
	    #4 0x66bf7b in read_populate_opts sequencer.c:2969
	    #5 0x6723f9 in sequencer_continue sequencer.c:5063
	    #6 0x4a4f74 in run_sequencer_rebase builtin/rebase.c:348
	    #7 0x4a64c8 in run_specific_rebase builtin/rebase.c:753
	    #8 0x4a9b8b in cmd_rebase builtin/rebase.c:1824
	    #9 0x407a32 in run_builtin git.c:466
	    #10 0x407e0a in handle_builtin git.c:721
	    #11 0x40803d in run_argv git.c:788
	    #12 0x40850f in cmd_main git.c:923
	    #13 0x4eee79 in main common-main.c:57
	    #14 0x7f2e8ca9f209 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
	    #15 0x7f2e8ca9f2bb in __libc_start_main_impl ../csu/libc-start.c:389
	    #16 0x405fd0 in _start (git+0x405fd0)

	Direct leak of 4 byte(s) in 1 object(s) allocated from:
	    #0 0x7f2e8cd45545 in __interceptor_malloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:75
	    #1 0x7f2e8cb0fcaa in __GI___strdup string/strdup.c:42
	    #2 0x6c4778 in xstrdup wrapper.c:39
	    #3 0x4a3c31 in xstrdup_or_null git-compat-util.h:1169
	    #4 0x4a447a in get_replay_opts builtin/rebase.c:163
	    #5 0x4a4f5b in run_sequencer_rebase builtin/rebase.c:346
	    #6 0x4a64c8 in run_specific_rebase builtin/rebase.c:753
	    #7 0x4a9b8b in cmd_rebase builtin/rebase.c:1824
	    #8 0x407a32 in run_builtin git.c:466
	    #9 0x407e0a in handle_builtin git.c:721
	    #10 0x40803d in run_argv git.c:788
	    #11 0x40850f in cmd_main git.c:923
	    #12 0x4eee79 in main common-main.c:57
	    #13 0x7f2e8ca9f209 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
	    #14 0x7f2e8ca9f2bb in __libc_start_main_impl ../csu/libc-start.c:389
	    #15 0x405fd0 in _start (git+0x405fd0)

This can be seen in e.g. the 4th test of
"t3404-rebase-interactive.sh".

In the larger picture the ownership of the "struct replay_opts" is
quite a mess, e.g. in this case rebase.c's static "get_replay_opts()"
function partially creates it, but nothing in rebase.c will free()
it. The structure is "mostly owned" by the sequencer API, but it also
expects to get these partially populated versions of it.

It would be better to have rebase keep track of what it allocated, and
free() that, and to pass that as a "const" to the sequencer API, which
would copy what it needs to its own version, and to free() that.

But doing so is a much larger change, and however messy the ownership
boundary is here is consistent with what we're doing already, so let's
just free() this to fix the leak.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
dscho pushed a commit that referenced this pull request Nov 21, 2022
When "read_strategy_opts()" is called we may have populated the
"opts->strategy" before, so we'll need to free() it to avoid leaking
memory.

We populate it before because we cal get_replay_opts() from within
"rebase.c" with an already populated "opts", which we then copy. Then
if we're doing a "rebase -i" the sequencer API itself will promptly
clobber our alloc'd version of it with its own.

If this code is changed to do, instead of the added free() here a:

	if (opts->strategy)
		opts->strategy = xstrdup("another leak");

We get a couple of stacktraces from -fsanitize=leak showing how we
ended up clobbering the already allocated value, i.e.:

	Direct leak of 6 byte(s) in 1 object(s) allocated from:
	    #0 0x7f2e8cd45545 in __interceptor_malloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:75
	    #1 0x7f2e8cb0fcaa in __GI___strdup string/strdup.c:42
	    #2 0x6c4778 in xstrdup wrapper.c:39
	    #3 0x66bcb8 in read_strategy_opts sequencer.c:2902
	    #4 0x66bf7b in read_populate_opts sequencer.c:2969
	    #5 0x6723f9 in sequencer_continue sequencer.c:5063
	    #6 0x4a4f74 in run_sequencer_rebase builtin/rebase.c:348
	    #7 0x4a64c8 in run_specific_rebase builtin/rebase.c:753
	    #8 0x4a9b8b in cmd_rebase builtin/rebase.c:1824
	    #9 0x407a32 in run_builtin git.c:466
	    #10 0x407e0a in handle_builtin git.c:721
	    #11 0x40803d in run_argv git.c:788
	    #12 0x40850f in cmd_main git.c:923
	    #13 0x4eee79 in main common-main.c:57
	    #14 0x7f2e8ca9f209 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
	    #15 0x7f2e8ca9f2bb in __libc_start_main_impl ../csu/libc-start.c:389
	    #16 0x405fd0 in _start (git+0x405fd0)

	Direct leak of 4 byte(s) in 1 object(s) allocated from:
	    #0 0x7f2e8cd45545 in __interceptor_malloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:75
	    #1 0x7f2e8cb0fcaa in __GI___strdup string/strdup.c:42
	    #2 0x6c4778 in xstrdup wrapper.c:39
	    #3 0x4a3c31 in xstrdup_or_null git-compat-util.h:1169
	    #4 0x4a447a in get_replay_opts builtin/rebase.c:163
	    #5 0x4a4f5b in run_sequencer_rebase builtin/rebase.c:346
	    #6 0x4a64c8 in run_specific_rebase builtin/rebase.c:753
	    #7 0x4a9b8b in cmd_rebase builtin/rebase.c:1824
	    #8 0x407a32 in run_builtin git.c:466
	    #9 0x407e0a in handle_builtin git.c:721
	    #10 0x40803d in run_argv git.c:788
	    #11 0x40850f in cmd_main git.c:923
	    #12 0x4eee79 in main common-main.c:57
	    #13 0x7f2e8ca9f209 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
	    #14 0x7f2e8ca9f2bb in __libc_start_main_impl ../csu/libc-start.c:389
	    #15 0x405fd0 in _start (git+0x405fd0)

This can be seen in e.g. the 4th test of
"t3404-rebase-interactive.sh".

In the larger picture the ownership of the "struct replay_opts" is
quite a mess, e.g. in this case rebase.c's static "get_replay_opts()"
function partially creates it, but nothing in rebase.c will free()
it. The structure is "mostly owned" by the sequencer API, but it also
expects to get these partially populated versions of it.

It would be better to have rebase keep track of what it allocated, and
free() that, and to pass that as a "const" to the sequencer API, which
would copy what it needs to its own version, and to free() that.

But doing so is a much larger change, and however messy the ownership
boundary is here is consistent with what we're doing already, so let's
just free() this to fix the leak.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
dscho pushed a commit that referenced this pull request Jan 17, 2023
There is an out-of-bounds read possible when parsing gitattributes that
have an attribute that is 2^31+1 bytes long. This is caused due to an
integer overflow when we assign the result of strlen(3P) to an `int`,
where we use the wrapped-around value in a subsequent call to
memcpy(3P). The following code reproduces the issue:

    blob=$(perl -e 'print "a" x 2147483649 . " attr"' | git hash-object -w --stdin)
    git update-index --add --cacheinfo 100644,$blob,.gitattributes
    git check-attr --all file

    AddressSanitizer:DEADLYSIGNAL
    =================================================================
    ==8451==ERROR: AddressSanitizer: SEGV on unknown address 0x7f93efa00800 (pc 0x7f94f1f8f082 bp 0x7ffddb59b3a0 sp 0x7ffddb59ab28 T0)
    ==8451==The signal is caused by a READ memory access.
        #0 0x7f94f1f8f082  (/usr/lib/libc.so.6+0x176082)
        #1 0x7f94f2047d9c in __interceptor_strspn /usr/src/debug/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:752
        #2 0x560e190f7f26 in parse_attr_line attr.c:375
        #3 0x560e190f9663 in handle_attr_line attr.c:660
        #4 0x560e190f9ddd in read_attr_from_index attr.c:769
        #5 0x560e190f9f14 in read_attr attr.c:797
        #6 0x560e190fa24e in bootstrap_attr_stack attr.c:867
        #7 0x560e190fa4a5 in prepare_attr_stack attr.c:902
        #8 0x560e190fb5dc in collect_some_attrs attr.c:1097
        #9 0x560e190fb93f in git_all_attrs attr.c:1128
        #10 0x560e18e6136e in check_attr builtin/check-attr.c:67
        #11 0x560e18e61c12 in cmd_check_attr builtin/check-attr.c:183
        #12 0x560e18e15993 in run_builtin git.c:466
        #13 0x560e18e16397 in handle_builtin git.c:721
        #14 0x560e18e16b2b in run_argv git.c:788
        #15 0x560e18e17991 in cmd_main git.c:926
        #16 0x560e190ae2bd in main common-main.c:57
        #17 0x7f94f1e3c28f  (/usr/lib/libc.so.6+0x2328f)
        #18 0x7f94f1e3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #19 0x560e18e110e4 in _start ../sysdeps/x86_64/start.S:115

    AddressSanitizer can not provide additional info.
    SUMMARY: AddressSanitizer: SEGV (/usr/lib/libc.so.6+0x176082)
    ==8451==ABORTING

Fix this bug by converting the variable to a `size_t` instead.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho pushed a commit that referenced this pull request Jan 17, 2023
It is possible to trigger an integer overflow when parsing attribute
names when there are more than 2^31 of them for a single pattern. This
can either lead to us dying due to trying to request too many bytes:

     blob=$(perl -e 'print "f" . " a=" x 2147483649' | git hash-object -w --stdin)
     git update-index --add --cacheinfo 100644,$blob,.gitattributes
     git attr-check --all file

    =================================================================
    ==1022==ERROR: AddressSanitizer: requested allocation size 0xfffffff800000032 (0xfffffff800001038 after adjustments for alignment, red zones etc.) exceeds maximum supported size of 0x10000000000 (thread T0)
        #0 0x7fd3efabf411 in __interceptor_calloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:77
        #1 0x5563a0a1e3d3 in xcalloc wrapper.c:150
        #2 0x5563a058d005 in parse_attr_line attr.c:384
        #3 0x5563a058e661 in handle_attr_line attr.c:660
        #4 0x5563a058eddb in read_attr_from_index attr.c:769
        #5 0x5563a058ef12 in read_attr attr.c:797
        #6 0x5563a058f24c in bootstrap_attr_stack attr.c:867
        #7 0x5563a058f4a3 in prepare_attr_stack attr.c:902
        #8 0x5563a05905da in collect_some_attrs attr.c:1097
        #9 0x5563a059093d in git_all_attrs attr.c:1128
        #10 0x5563a02f636e in check_attr builtin/check-attr.c:67
        #11 0x5563a02f6c12 in cmd_check_attr builtin/check-attr.c:183
        #12 0x5563a02aa993 in run_builtin git.c:466
        #13 0x5563a02ab397 in handle_builtin git.c:721
        #14 0x5563a02abb2b in run_argv git.c:788
        #15 0x5563a02ac991 in cmd_main git.c:926
        #16 0x5563a05432bd in main common-main.c:57
        #17 0x7fd3ef82228f  (/usr/lib/libc.so.6+0x2328f)

    ==1022==HINT: if you don't care about these errors you may set allocator_may_return_null=1
    SUMMARY: AddressSanitizer: allocation-size-too-big /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:77 in __interceptor_calloc
    ==1022==ABORTING

Or, much worse, it can lead to an out-of-bounds write because we
underallocate and then memcpy(3P) into an array:

    perl -e '
        print "A " . "\rh="x2000000000;
        print "\rh="x2000000000;
        print "\rh="x294967294 . "\n"
    ' >.gitattributes
    git add .gitattributes
    git commit -am "evil attributes"

    $ git clone --quiet /path/to/repo
    =================================================================
    ==15062==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000002550 at pc 0x5555559884d5 bp 0x7fffffffbc60 sp 0x7fffffffbc58
    WRITE of size 8 at 0x602000002550 thread T0
        #0 0x5555559884d4 in parse_attr_line attr.c:393
        #1 0x5555559884d4 in handle_attr_line attr.c:660
        #2 0x555555988902 in read_attr_from_index attr.c:784
        #3 0x555555988902 in read_attr_from_index attr.c:747
        #4 0x555555988a1d in read_attr attr.c:800
        #5 0x555555989b0c in bootstrap_attr_stack attr.c:882
        #6 0x555555989b0c in prepare_attr_stack attr.c:917
        #7 0x555555989b0c in collect_some_attrs attr.c:1112
        #8 0x55555598b141 in git_check_attr attr.c:1126
        #9 0x555555a13004 in convert_attrs convert.c:1311
        #10 0x555555a95e04 in checkout_entry_ca entry.c:553
        #11 0x555555d58bf6 in checkout_entry entry.h:42
        #12 0x555555d58bf6 in check_updates unpack-trees.c:480
        #13 0x555555d5eb55 in unpack_trees unpack-trees.c:2040
        #14 0x555555785ab7 in checkout builtin/clone.c:724
        #15 0x555555785ab7 in cmd_clone builtin/clone.c:1384
        #16 0x55555572443c in run_builtin git.c:466
        #17 0x55555572443c in handle_builtin git.c:721
        #18 0x555555727872 in run_argv git.c:788
        #19 0x555555727872 in cmd_main git.c:926
        #20 0x555555721fa0 in main common-main.c:57
        #21 0x7ffff73f1d09 in __libc_start_main ../csu/libc-start.c:308
        #22 0x555555723f39 in _start (git+0x1cff39)

    0x602000002552 is located 0 bytes to the right of 2-byte region [0x602000002550,0x602000002552) allocated by thread T0 here:
        #0 0x7ffff768c037 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:154
        #1 0x555555d7fff7 in xcalloc wrapper.c:150
        #2 0x55555598815f in parse_attr_line attr.c:384
        #3 0x55555598815f in handle_attr_line attr.c:660
        #4 0x555555988902 in read_attr_from_index attr.c:784
        #5 0x555555988902 in read_attr_from_index attr.c:747
        #6 0x555555988a1d in read_attr attr.c:800
        #7 0x555555989b0c in bootstrap_attr_stack attr.c:882
        #8 0x555555989b0c in prepare_attr_stack attr.c:917
        #9 0x555555989b0c in collect_some_attrs attr.c:1112
        #10 0x55555598b141 in git_check_attr attr.c:1126
        #11 0x555555a13004 in convert_attrs convert.c:1311
        #12 0x555555a95e04 in checkout_entry_ca entry.c:553
        #13 0x555555d58bf6 in checkout_entry entry.h:42
        #14 0x555555d58bf6 in check_updates unpack-trees.c:480
        #15 0x555555d5eb55 in unpack_trees unpack-trees.c:2040
        #16 0x555555785ab7 in checkout builtin/clone.c:724
        #17 0x555555785ab7 in cmd_clone builtin/clone.c:1384
        #18 0x55555572443c in run_builtin git.c:466
        #19 0x55555572443c in handle_builtin git.c:721
        #20 0x555555727872 in run_argv git.c:788
        #21 0x555555727872 in cmd_main git.c:926
        #22 0x555555721fa0 in main common-main.c:57
        #23 0x7ffff73f1d09 in __libc_start_main ../csu/libc-start.c:308

    SUMMARY: AddressSanitizer: heap-buffer-overflow attr.c:393 in parse_attr_line
    Shadow bytes around the buggy address:
      0x0c047fff8450: fa fa 00 02 fa fa 00 07 fa fa fd fd fa fa 00 00
      0x0c047fff8460: fa fa 02 fa fa fa fd fd fa fa 00 06 fa fa 05 fa
      0x0c047fff8470: fa fa fd fd fa fa 00 02 fa fa 06 fa fa fa 05 fa
      0x0c047fff8480: fa fa 07 fa fa fa fd fd fa fa 00 01 fa fa 00 02
      0x0c047fff8490: fa fa 00 03 fa fa 00 fa fa fa 00 01 fa fa 00 03
    =>0x0c047fff84a0: fa fa 00 01 fa fa 00 02 fa fa[02]fa fa fa fa fa
      0x0c047fff84b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c047fff84c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c047fff84d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c047fff84e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c047fff84f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
    Shadow byte legend (one shadow byte represents 8 application bytes):
      Addressable:           00
      Partially addressable: 01 02 03 04 05 06 07
      Heap left redzone:       fa
      Freed heap region:       fd
      Stack left redzone:      f1
      Stack mid redzone:       f2
      Stack right redzone:     f3
      Stack after return:      f5
      Stack use after scope:   f8
      Global redzone:          f9
      Global init order:       f6
      Poisoned by user:        f7
      Container overflow:      fc
      Array cookie:            ac
      Intra object redzone:    bb
      ASan internal:           fe
      Left alloca redzone:     ca
      Right alloca redzone:    cb
      Shadow gap:              cc
    ==15062==ABORTING

Fix this bug by using `size_t` instead to count the number of attributes
so that this value cannot reasonably overflow without running out of
memory before already.

Reported-by: Markus Vervier <markus.vervier@x41-dsec.de>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho pushed a commit that referenced this pull request Jan 17, 2023
When using a padding specifier in the pretty format passed to git-log(1)
we need to calculate the string length in several places. These string
lengths are stored in `int`s though, which means that these can easily
overflow when the input lengths exceeds 2GB. This can ultimately lead to
an out-of-bounds write when these are used in a call to memcpy(3P):

        ==8340==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7f1ec62f97fe at pc 0x7f2127e5f427 bp 0x7ffd3bd63de0 sp 0x7ffd3bd63588
    WRITE of size 1 at 0x7f1ec62f97fe thread T0
        #0 0x7f2127e5f426 in __interceptor_memcpy /usr/src/debug/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:827
        #1 0x5628e96aa605 in format_and_pad_commit pretty.c:1762
        #2 0x5628e96aa7f4 in format_commit_item pretty.c:1801
        #3 0x5628e97cdb24 in strbuf_expand strbuf.c:429
        #4 0x5628e96ab060 in repo_format_commit_message pretty.c:1869
        #5 0x5628e96acd0f in pretty_print_commit pretty.c:2161
        #6 0x5628e95a44c8 in show_log log-tree.c:781
        #7 0x5628e95a76ba in log_tree_commit log-tree.c:1117
        #8 0x5628e922bed5 in cmd_log_walk_no_free builtin/log.c:508
        #9 0x5628e922c35b in cmd_log_walk builtin/log.c:549
        #10 0x5628e922f1a2 in cmd_log builtin/log.c:883
        #11 0x5628e9106993 in run_builtin git.c:466
        #12 0x5628e9107397 in handle_builtin git.c:721
        #13 0x5628e9107b07 in run_argv git.c:788
        #14 0x5628e91088a7 in cmd_main git.c:923
        #15 0x5628e939d682 in main common-main.c:57
        #16 0x7f2127c3c28f  (/usr/lib/libc.so.6+0x2328f)
        #17 0x7f2127c3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #18 0x5628e91020e4 in _start ../sysdeps/x86_64/start.S:115

    0x7f1ec62f97fe is located 2 bytes to the left of 4831838265-byte region [0x7f1ec62f9800,0x7f1fe62f9839)
    allocated by thread T0 here:
        #0 0x7f2127ebe7ea in __interceptor_realloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:85
        #1 0x5628e98774d4 in xrealloc wrapper.c:136
        #2 0x5628e97cb01c in strbuf_grow strbuf.c:99
        #3 0x5628e97ccd42 in strbuf_addchars strbuf.c:327
        #4 0x5628e96aa55c in format_and_pad_commit pretty.c:1761
        #5 0x5628e96aa7f4 in format_commit_item pretty.c:1801
        #6 0x5628e97cdb24 in strbuf_expand strbuf.c:429
        #7 0x5628e96ab060 in repo_format_commit_message pretty.c:1869
        #8 0x5628e96acd0f in pretty_print_commit pretty.c:2161
        #9 0x5628e95a44c8 in show_log log-tree.c:781
        #10 0x5628e95a76ba in log_tree_commit log-tree.c:1117
        #11 0x5628e922bed5 in cmd_log_walk_no_free builtin/log.c:508
        #12 0x5628e922c35b in cmd_log_walk builtin/log.c:549
        #13 0x5628e922f1a2 in cmd_log builtin/log.c:883
        #14 0x5628e9106993 in run_builtin git.c:466
        #15 0x5628e9107397 in handle_builtin git.c:721
        #16 0x5628e9107b07 in run_argv git.c:788
        #17 0x5628e91088a7 in cmd_main git.c:923
        #18 0x5628e939d682 in main common-main.c:57
        #19 0x7f2127c3c28f  (/usr/lib/libc.so.6+0x2328f)
        #20 0x7f2127c3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #21 0x5628e91020e4 in _start ../sysdeps/x86_64/start.S:115

    SUMMARY: AddressSanitizer: heap-buffer-overflow /usr/src/debug/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:827 in __interceptor_memcpy
    Shadow bytes around the buggy address:
      0x0fe458c572a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0fe458c572b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0fe458c572c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0fe458c572d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0fe458c572e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
    =>0x0fe458c572f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa[fa]
      0x0fe458c57300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
      0x0fe458c57310: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
      0x0fe458c57320: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
      0x0fe458c57330: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
      0x0fe458c57340: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    Shadow byte legend (one shadow byte represents 8 application bytes):
      Addressable:           00
      Partially addressable: 01 02 03 04 05 06 07
      Heap left redzone:       fa
      Freed heap region:       fd
      Stack left redzone:      f1
      Stack mid redzone:       f2
      Stack right redzone:     f3
      Stack after return:      f5
      Stack use after scope:   f8
      Global redzone:          f9
      Global init order:       f6
      Poisoned by user:        f7
      Container overflow:      fc
      Array cookie:            ac
      Intra object redzone:    bb
      ASan internal:           fe
      Left alloca redzone:     ca
      Right alloca redzone:    cb
    ==8340==ABORTING

The pretty format can also be used in `git archive` operations via the
`export-subst` attribute. So this is what in our opinion makes this a
critical issue in the context of Git forges which allow to download an
archive of user supplied Git repositories.

Fix this vulnerability by using `size_t` instead of `int` to track the
string lengths. Add tests which detect this vulnerability when Git is
compiled with the address sanitizer.

Reported-by: Joern Schneeweisz <jschneeweisz@gitlab.com>
Original-patch-by: Joern Schneeweisz <jschneeweisz@gitlab.com>
Modified-by: Taylor  Blau <me@ttalorr.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho pushed a commit that referenced this pull request Jan 17, 2023
With the `%>>(<N>)` pretty formatter, you can ask git-log(1) et al to
steal spaces. To do so we need to look ahead of the next token to see
whether there are spaces there. This loop takes into account ANSI
sequences that end with an `m`, and if it finds any it will skip them
until it finds the first space. While doing so it does not take into
account the buffer's limits though and easily does an out-of-bounds
read.

Add a test that hits this behaviour. While we don't have an easy way to
verify this, the test causes the following failure when run with
`SANITIZE=address`:

    ==37941==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x603000000baf at pc 0x55ba6f88e0d0 bp 0x7ffc84c50d20 sp 0x7ffc84c50d10
    READ of size 1 at 0x603000000baf thread T0
        #0 0x55ba6f88e0cf in format_and_pad_commit pretty.c:1712
        #1 0x55ba6f88e7b4 in format_commit_item pretty.c:1801
        #2 0x55ba6f9b1ae4 in strbuf_expand strbuf.c:429
        #3 0x55ba6f88f020 in repo_format_commit_message pretty.c:1869
        #4 0x55ba6f890ccf in pretty_print_commit pretty.c:2161
        #5 0x55ba6f7884c8 in show_log log-tree.c:781
        #6 0x55ba6f78b6ba in log_tree_commit log-tree.c:1117
        #7 0x55ba6f40fed5 in cmd_log_walk_no_free builtin/log.c:508
        #8 0x55ba6f41035b in cmd_log_walk builtin/log.c:549
        #9 0x55ba6f4131a2 in cmd_log builtin/log.c:883
        #10 0x55ba6f2ea993 in run_builtin git.c:466
        #11 0x55ba6f2eb397 in handle_builtin git.c:721
        #12 0x55ba6f2ebb07 in run_argv git.c:788
        #13 0x55ba6f2ec8a7 in cmd_main git.c:923
        #14 0x55ba6f581682 in main common-main.c:57
        #15 0x7f2d08c3c28f  (/usr/lib/libc.so.6+0x2328f)
        #16 0x7f2d08c3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #17 0x55ba6f2e60e4 in _start ../sysdeps/x86_64/start.S:115

    0x603000000baf is located 1 bytes to the left of 24-byte region [0x603000000bb0,0x603000000bc8)
    allocated by thread T0 here:
        #0 0x7f2d08ebe7ea in __interceptor_realloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:85
        #1 0x55ba6fa5b494 in xrealloc wrapper.c:136
        #2 0x55ba6f9aefdc in strbuf_grow strbuf.c:99
        #3 0x55ba6f9b0a06 in strbuf_add strbuf.c:298
        #4 0x55ba6f9b1a25 in strbuf_expand strbuf.c:418
        #5 0x55ba6f88f020 in repo_format_commit_message pretty.c:1869
        #6 0x55ba6f890ccf in pretty_print_commit pretty.c:2161
        #7 0x55ba6f7884c8 in show_log log-tree.c:781
        #8 0x55ba6f78b6ba in log_tree_commit log-tree.c:1117
        #9 0x55ba6f40fed5 in cmd_log_walk_no_free builtin/log.c:508
        #10 0x55ba6f41035b in cmd_log_walk builtin/log.c:549
        #11 0x55ba6f4131a2 in cmd_log builtin/log.c:883
        #12 0x55ba6f2ea993 in run_builtin git.c:466
        #13 0x55ba6f2eb397 in handle_builtin git.c:721
        #14 0x55ba6f2ebb07 in run_argv git.c:788
        #15 0x55ba6f2ec8a7 in cmd_main git.c:923
        #16 0x55ba6f581682 in main common-main.c:57
        #17 0x7f2d08c3c28f  (/usr/lib/libc.so.6+0x2328f)
        #18 0x7f2d08c3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #19 0x55ba6f2e60e4 in _start ../sysdeps/x86_64/start.S:115

    SUMMARY: AddressSanitizer: heap-buffer-overflow pretty.c:1712 in format_and_pad_commit
    Shadow bytes around the buggy address:
      0x0c067fff8120: fa fa fd fd fd fa fa fa fd fd fd fa fa fa fd fd
      0x0c067fff8130: fd fd fa fa fd fd fd fd fa fa fd fd fd fa fa fa
      0x0c067fff8140: fd fd fd fa fa fa fd fd fd fa fa fa fd fd fd fa
      0x0c067fff8150: fa fa fd fd fd fd fa fa 00 00 00 fa fa fa fd fd
      0x0c067fff8160: fd fa fa fa fd fd fd fa fa fa fd fd fd fa fa fa
    =>0x0c067fff8170: fd fd fd fa fa[fa]00 00 00 fa fa fa 00 00 00 fa
      0x0c067fff8180: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff8190: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff81a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff81b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff81c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
    Shadow byte legend (one shadow byte represents 8 application bytes):
      Addressable:           00
      Partially addressable: 01 02 03 04 05 06 07
      Heap left redzone:       fa
      Freed heap region:       fd
      Stack left redzone:      f1
      Stack mid redzone:       f2
      Stack right redzone:     f3
      Stack after return:      f5
      Stack use after scope:   f8
      Global redzone:          f9
      Global init order:       f6
      Poisoned by user:        f7
      Container overflow:      fc
      Array cookie:            ac
      Intra object redzone:    bb
      ASan internal:           fe
      Left alloca redzone:     ca
      Right alloca redzone:    cb

Luckily enough, this would only cause us to copy the out-of-bounds data
into the formatted commit in case we really had an ANSI sequence
preceding our buffer. So this bug likely has no security consequences.

Fix it regardless by not traversing past the buffer's start.

Reported-by: Patrick Steinhardt <ps@pks.im>
Reported-by: Eric Sesterhenn <eric.sesterhenn@x41-dsec.de>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho pushed a commit that referenced this pull request Jan 17, 2023
An out-of-bounds read can be triggered when parsing an incomplete
padding format string passed via `--pretty=format` or in Git archives
when files are marked with the `export-subst` gitattribute.

This bug exists since we have introduced support for truncating output
via the `trunc` keyword a7f01c6 (pretty: support truncating in %>, %<
and %><, 2013-04-19). Before this commit, we used to find the end of the
formatting string by using strchr(3P). This function returns a `NULL`
pointer in case the character in question wasn't found. The subsequent
check whether any character was found thus simply checked the returned
pointer. After the commit we switched to strcspn(3P) though, which only
returns the offset to the first found character or to the trailing NUL
byte. As the end pointer is now computed by adding the offset to the
start pointer it won't be `NULL` anymore, and as a consequence the check
doesn't do anything anymore.

The out-of-bounds data that is being read can in fact end up in the
formatted string. As a consequence, it is possible to leak memory
contents either by calling git-log(1) or via git-archive(1) when any of
the archived files is marked with the `export-subst` gitattribute.

    ==10888==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000398 at pc 0x7f0356047cb2 bp 0x7fff3ffb95d0 sp 0x7fff3ffb8d78
    READ of size 1 at 0x602000000398 thread T0
        #0 0x7f0356047cb1 in __interceptor_strchrnul /usr/src/debug/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:725
        #1 0x563b7cec9a43 in strbuf_expand strbuf.c:417
        #2 0x563b7cda7060 in repo_format_commit_message pretty.c:1869
        #3 0x563b7cda8d0f in pretty_print_commit pretty.c:2161
        #4 0x563b7cca04c8 in show_log log-tree.c:781
        #5 0x563b7cca36ba in log_tree_commit log-tree.c:1117
        #6 0x563b7c927ed5 in cmd_log_walk_no_free builtin/log.c:508
        #7 0x563b7c92835b in cmd_log_walk builtin/log.c:549
        #8 0x563b7c92b1a2 in cmd_log builtin/log.c:883
        #9 0x563b7c802993 in run_builtin git.c:466
        #10 0x563b7c803397 in handle_builtin git.c:721
        #11 0x563b7c803b07 in run_argv git.c:788
        #12 0x563b7c8048a7 in cmd_main git.c:923
        #13 0x563b7ca99682 in main common-main.c:57
        #14 0x7f0355e3c28f  (/usr/lib/libc.so.6+0x2328f)
        #15 0x7f0355e3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #16 0x563b7c7fe0e4 in _start ../sysdeps/x86_64/start.S:115

    0x602000000398 is located 0 bytes to the right of 8-byte region [0x602000000390,0x602000000398)
    allocated by thread T0 here:
        #0 0x7f0356072faa in __interceptor_strdup /usr/src/debug/gcc/libsanitizer/asan/asan_interceptors.cpp:439
        #1 0x563b7cf7317c in xstrdup wrapper.c:39
        #2 0x563b7cd9a06a in save_user_format pretty.c:40
        #3 0x563b7cd9b3e5 in get_commit_format pretty.c:173
        #4 0x563b7ce54ea0 in handle_revision_opt revision.c:2456
        #5 0x563b7ce597c9 in setup_revisions revision.c:2850
        #6 0x563b7c9269e0 in cmd_log_init_finish builtin/log.c:269
        #7 0x563b7c927362 in cmd_log_init builtin/log.c:348
        #8 0x563b7c92b193 in cmd_log builtin/log.c:882
        #9 0x563b7c802993 in run_builtin git.c:466
        #10 0x563b7c803397 in handle_builtin git.c:721
        #11 0x563b7c803b07 in run_argv git.c:788
        #12 0x563b7c8048a7 in cmd_main git.c:923
        #13 0x563b7ca99682 in main common-main.c:57
        #14 0x7f0355e3c28f  (/usr/lib/libc.so.6+0x2328f)
        #15 0x7f0355e3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #16 0x563b7c7fe0e4 in _start ../sysdeps/x86_64/start.S:115

    SUMMARY: AddressSanitizer: heap-buffer-overflow /usr/src/debug/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:725 in __interceptor_strchrnul
    Shadow bytes around the buggy address:
      0x0c047fff8020: fa fa fd fd fa fa 00 06 fa fa 05 fa fa fa fd fd
      0x0c047fff8030: fa fa 00 02 fa fa 06 fa fa fa 05 fa fa fa fd fd
      0x0c047fff8040: fa fa 00 07 fa fa 03 fa fa fa fd fd fa fa 00 00
      0x0c047fff8050: fa fa 00 01 fa fa fd fd fa fa 00 00 fa fa 00 01
      0x0c047fff8060: fa fa 00 06 fa fa 00 06 fa fa 05 fa fa fa 05 fa
    =>0x0c047fff8070: fa fa 00[fa]fa fa fd fa fa fa fd fd fa fa fd fd
      0x0c047fff8080: fa fa fd fd fa fa 00 00 fa fa 00 fa fa fa fd fa
      0x0c047fff8090: fa fa fd fd fa fa 00 00 fa fa fa fa fa fa fa fa
      0x0c047fff80a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c047fff80b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c047fff80c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
    Shadow byte legend (one shadow byte represents 8 application bytes):
      Addressable:           00
      Partially addressable: 01 02 03 04 05 06 07
      Heap left redzone:       fa
      Freed heap region:       fd
      Stack left redzone:      f1
      Stack mid redzone:       f2
      Stack right redzone:     f3
      Stack after return:      f5
      Stack use after scope:   f8
      Global redzone:          f9
      Global init order:       f6
      Poisoned by user:        f7
      Container overflow:      fc
      Array cookie:            ac
      Intra object redzone:    bb
      ASan internal:           fe
      Left alloca redzone:     ca
      Right alloca redzone:    cb
    ==10888==ABORTING

Fix this bug by checking whether `end` points at the trailing NUL byte.
Add a test which catches this out-of-bounds read and which demonstrates
that we used to write out-of-bounds data into the formatted message.

Reported-by: Markus Vervier <markus.vervier@x41-dsec.de>
Original-patch-by: Markus Vervier <markus.vervier@x41-dsec.de>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho pushed a commit that referenced this pull request Jan 17, 2023
The return type of both `utf8_strwidth()` and `utf8_strnwidth()` is
`int`, but we operate on string lengths which are typically of type
`size_t`. This means that when the string is longer than `INT_MAX`, we
will overflow and thus return a negative result.

This can lead to an out-of-bounds write with `--pretty=format:%<1)%B`
and a commit message that is 2^31+1 bytes long:

    =================================================================
    ==26009==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x603000001168 at pc 0x7f95c4e5f427 bp 0x7ffd8541c900 sp 0x7ffd8541c0a8
    WRITE of size 2147483649 at 0x603000001168 thread T0
        #0 0x7f95c4e5f426 in __interceptor_memcpy /usr/src/debug/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:827
        #1 0x5612bbb1068c in format_and_pad_commit pretty.c:1763
        #2 0x5612bbb1087a in format_commit_item pretty.c:1801
        #3 0x5612bbc33bab in strbuf_expand strbuf.c:429
        #4 0x5612bbb110e7 in repo_format_commit_message pretty.c:1869
        #5 0x5612bbb12d96 in pretty_print_commit pretty.c:2161
        #6 0x5612bba0a4d5 in show_log log-tree.c:781
        #7 0x5612bba0d6c7 in log_tree_commit log-tree.c:1117
        #8 0x5612bb691ed5 in cmd_log_walk_no_free builtin/log.c:508
        #9 0x5612bb69235b in cmd_log_walk builtin/log.c:549
        #10 0x5612bb6951a2 in cmd_log builtin/log.c:883
        #11 0x5612bb56c993 in run_builtin git.c:466
        #12 0x5612bb56d397 in handle_builtin git.c:721
        #13 0x5612bb56db07 in run_argv git.c:788
        #14 0x5612bb56e8a7 in cmd_main git.c:923
        #15 0x5612bb803682 in main common-main.c:57
        #16 0x7f95c4c3c28f  (/usr/lib/libc.so.6+0x2328f)
        #17 0x7f95c4c3c349 in __libc_start_main (/usr/lib/libc.so.6+0x23349)
        #18 0x5612bb5680e4 in _start ../sysdeps/x86_64/start.S:115

    0x603000001168 is located 0 bytes to the right of 24-byte region [0x603000001150,0x603000001168)
    allocated by thread T0 here:
        #0 0x7f95c4ebe7ea in __interceptor_realloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:85
        #1 0x5612bbcdd556 in xrealloc wrapper.c:136
        #2 0x5612bbc310a3 in strbuf_grow strbuf.c:99
        #3 0x5612bbc32acd in strbuf_add strbuf.c:298
        #4 0x5612bbc33aec in strbuf_expand strbuf.c:418
        #5 0x5612bbb110e7 in repo_format_commit_message pretty.c:1869
        #6 0x5612bbb12d96 in pretty_print_commit pretty.c:2161
        #7 0x5612bba0a4d5 in show_log log-tree.c:781
        #8 0x5612bba0d6c7 in log_tree_commit log-tree.c:1117
        #9 0x5612bb691ed5 in cmd_log_walk_no_free builtin/log.c:508
        #10 0x5612bb69235b in cmd_log_walk builtin/log.c:549
        #11 0x5612bb6951a2 in cmd_log builtin/log.c:883
        #12 0x5612bb56c993 in run_builtin git.c:466
        #13 0x5612bb56d397 in handle_builtin git.c:721
        #14 0x5612bb56db07 in run_argv git.c:788
        #15 0x5612bb56e8a7 in cmd_main git.c:923
        #16 0x5612bb803682 in main common-main.c:57
        #17 0x7f95c4c3c28f  (/usr/lib/libc.so.6+0x2328f)

    SUMMARY: AddressSanitizer: heap-buffer-overflow /usr/src/debug/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:827 in __interceptor_memcpy
    Shadow bytes around the buggy address:
      0x0c067fff81d0: fd fd fd fa fa fa fd fd fd fa fa fa fd fd fd fa
      0x0c067fff81e0: fa fa fd fd fd fd fa fa fd fd fd fd fa fa fd fd
      0x0c067fff81f0: fd fa fa fa fd fd fd fa fa fa fd fd fd fa fa fa
      0x0c067fff8200: fd fd fd fa fa fa fd fd fd fd fa fa 00 00 00 fa
      0x0c067fff8210: fa fa fd fd fd fa fa fa fd fd fd fa fa fa fd fd
    =>0x0c067fff8220: fd fa fa fa fd fd fd fa fa fa 00 00 00[fa]fa fa
      0x0c067fff8230: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff8240: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff8250: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff8260: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
      0x0c067fff8270: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
    Shadow byte legend (one shadow byte represents 8 application bytes):
      Addressable:           00
      Partially addressable: 01 02 03 04 05 06 07
      Heap left redzone:       fa
      Freed heap region:       fd
      Stack left redzone:      f1
      Stack mid redzone:       f2
      Stack right redzone:     f3
      Stack after return:      f5
      Stack use after scope:   f8
      Global redzone:          f9
      Global init order:       f6
      Poisoned by user:        f7
      Container overflow:      fc
      Array cookie:            ac
      Intra object redzone:    bb
      ASan internal:           fe
      Left alloca redzone:     ca
      Right alloca redzone:    cb
    ==26009==ABORTING

Now the proper fix for this would be to convert both functions to return
an `size_t` instead of an `int`. But given that this commit may be part
of a security release, let's instead do the minimal viable fix and die
in case we see an overflow.

Add a test that would have previously caused us to crash.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho pushed a commit that referenced this pull request Aug 24, 2023
When t5583-push-branches.sh was originally introduced via 425b4d7
(push: introduce '--branches' option, 2023-05-06), it was not leak-free.
In fact, the test did not even run correctly until 022fbb6 (t5583:
fix shebang line, 2023-05-12), but after applying that patch, we see a
failure at t5583.8:

    ==2529087==ERROR: LeakSanitizer: detected memory leaks

    Direct leak of 384 byte(s) in 1 object(s) allocated from:
        #0 0x7fb536330986 in __interceptor_realloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:98
        #1 0x55e07606cbf9 in xrealloc wrapper.c:140
        #2 0x55e075fb6cb3 in prio_queue_put prio-queue.c:42
        #3 0x55e075ec81cb in get_reachable_subset commit-reach.c:917
        #4 0x55e075fe9cce in add_missing_tags remote.c:1518
        #5 0x55e075fea1e4 in match_push_refs remote.c:1665
        #6 0x55e076050a8e in transport_push transport.c:1378
        #7 0x55e075e2eb74 in push_with_options builtin/push.c:401
        #8 0x55e075e2edb0 in do_push builtin/push.c:458
        #9 0x55e075e2ff7a in cmd_push builtin/push.c:702
        #10 0x55e075d8aaf0 in run_builtin git.c:452
        #11 0x55e075d8af08 in handle_builtin git.c:706
        #12 0x55e075d8b12c in run_argv git.c:770
        #13 0x55e075d8b6a0 in cmd_main git.c:905
        #14 0x55e075e81f07 in main common-main.c:60
        #15 0x7fb5360ab6c9 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
        #16 0x7fb5360ab784 in __libc_start_main_impl ../csu/libc-start.c:360
        #17 0x55e075d88f40 in _start (git+0x1ff40) (BuildId: 38ad998b85a535e786129979443630d025ec2453)

    SUMMARY: LeakSanitizer: 384 byte(s) leaked in 1 allocation(s).

This leak was addressed independently via 68b5117 (commit-reach: fix
memory leak in get_reachable_subset(), 2023-06-03), which makes t5583
leak-free.

But t5583 was not in the tree when 68b5117 was written, and the two
only met after the latter was merged back in via 693bde4 (Merge
branch 'mh/commit-reach-get-reachable-plug-leak', 2023-06-20).

At that point, t5583 was leak-free. Let's mark it as such accordingly.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho pushed a commit that referenced this pull request Aug 29, 2023
When t5583-push-branches.sh was originally introduced via 425b4d7
(push: introduce '--branches' option, 2023-05-06), it was not leak-free.
In fact, the test did not even run correctly until 022fbb6 (t5583:
fix shebang line, 2023-05-12), but after applying that patch, we see a
failure at t5583.8:

    ==2529087==ERROR: LeakSanitizer: detected memory leaks

    Direct leak of 384 byte(s) in 1 object(s) allocated from:
        #0 0x7fb536330986 in __interceptor_realloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:98
        #1 0x55e07606cbf9 in xrealloc wrapper.c:140
        #2 0x55e075fb6cb3 in prio_queue_put prio-queue.c:42
        #3 0x55e075ec81cb in get_reachable_subset commit-reach.c:917
        #4 0x55e075fe9cce in add_missing_tags remote.c:1518
        #5 0x55e075fea1e4 in match_push_refs remote.c:1665
        #6 0x55e076050a8e in transport_push transport.c:1378
        #7 0x55e075e2eb74 in push_with_options builtin/push.c:401
        #8 0x55e075e2edb0 in do_push builtin/push.c:458
        #9 0x55e075e2ff7a in cmd_push builtin/push.c:702
        #10 0x55e075d8aaf0 in run_builtin git.c:452
        #11 0x55e075d8af08 in handle_builtin git.c:706
        #12 0x55e075d8b12c in run_argv git.c:770
        #13 0x55e075d8b6a0 in cmd_main git.c:905
        #14 0x55e075e81f07 in main common-main.c:60
        #15 0x7fb5360ab6c9 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
        #16 0x7fb5360ab784 in __libc_start_main_impl ../csu/libc-start.c:360
        #17 0x55e075d88f40 in _start (git+0x1ff40) (BuildId: 38ad998b85a535e786129979443630d025ec2453)

    SUMMARY: LeakSanitizer: 384 byte(s) leaked in 1 allocation(s).

This leak was addressed independently via 68b5117 (commit-reach: fix
memory leak in get_reachable_subset(), 2023-06-03), which makes t5583
leak-free.

But t5583 was not in the tree when 68b5117 was written, and the two
only met after the latter was merged back in via 693bde4 (Merge
branch 'mh/commit-reach-get-reachable-plug-leak', 2023-06-20).

At that point, t5583 was leak-free. Let's mark it as such accordingly.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Apr 29, 2024
gitgitgadget bot pushed a commit that referenced this pull request May 25, 2024
gitgitgadget bot pushed a commit that referenced this pull request Jun 17, 2024
Memory sanitizer (msan) is detecting a use of an uninitialized variable
(`size`) in `read_attr_from_index`:

    ==2268==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x5651f3416504 in read_attr_from_index git/attr.c:868:11
    #1 0x5651f3415530 in read_attr git/attr.c
    #2 0x5651f3413d74 in bootstrap_attr_stack git/attr.c:968:6
    #3 0x5651f3413d74 in prepare_attr_stack git/attr.c:1004:2
    #4 0x5651f3413d74 in collect_some_attrs git/attr.c:1199:2
    #5 0x5651f3413144 in git_check_attr git/attr.c:1345:2
    #6 0x5651f34728da in convert_attrs git/convert.c:1320:2
    #7 0x5651f3473425 in would_convert_to_git_filter_fd git/convert.c:1373:2
    #8 0x5651f357a35e in index_fd git/object-file.c:2630:34
    #9 0x5651f357aa15 in index_path git/object-file.c:2657:7
    #10 0x5651f35db9d9 in add_to_index git/read-cache.c:766:7
    #11 0x5651f35dc170 in add_file_to_index git/read-cache.c:799:9
    #12 0x5651f321f9b2 in add_files git/builtin/add.c:346:7
    #13 0x5651f321f9b2 in cmd_add git/builtin/add.c:565:18
    #14 0x5651f321d327 in run_builtin git/git.c:474:11
    #15 0x5651f321bc9e in handle_builtin git/git.c:729:3
    #16 0x5651f321a792 in run_argv git/git.c:793:4
    #17 0x5651f321a792 in cmd_main git/git.c:928:19
    #18 0x5651f33dde1f in main git/common-main.c:62:11

The issue exists because `size` is an output parameter from
`read_blob_data_from_index`, but it's only modified if
`read_blob_data_from_index` returns non-NULL. The read of `size` when
calling `read_attr_from_buf` unconditionally may read from an
uninitialized value. `read_attr_from_buf` checks that `buf` is non-NULL
before reading from `size`, but by then it's already too late: the
uninitialized read will have happened already. Furthermore, there's no
guarantee that the compiler won't reorder things so that it checks
`size` before checking `!buf`.

Make the call to `read_attr_from_buf` conditional on `buf` being
non-NULL, ensuring that `size` is not read if it's never set.

Signed-off-by: Kyle Lippincott <spectral@google.com>
gitgitgadget bot pushed a commit that referenced this pull request Jun 17, 2024
Memory sanitizer (msan) is detecting a use of an uninitialized variable
(`size`) in `read_attr_from_index`:

    ==2268==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x5651f3416504 in read_attr_from_index git/attr.c:868:11
    #1 0x5651f3415530 in read_attr git/attr.c
    #2 0x5651f3413d74 in bootstrap_attr_stack git/attr.c:968:6
    #3 0x5651f3413d74 in prepare_attr_stack git/attr.c:1004:2
    #4 0x5651f3413d74 in collect_some_attrs git/attr.c:1199:2
    #5 0x5651f3413144 in git_check_attr git/attr.c:1345:2
    #6 0x5651f34728da in convert_attrs git/convert.c:1320:2
    #7 0x5651f3473425 in would_convert_to_git_filter_fd git/convert.c:1373:2
    #8 0x5651f357a35e in index_fd git/object-file.c:2630:34
    #9 0x5651f357aa15 in index_path git/object-file.c:2657:7
    #10 0x5651f35db9d9 in add_to_index git/read-cache.c:766:7
    #11 0x5651f35dc170 in add_file_to_index git/read-cache.c:799:9
    #12 0x5651f321f9b2 in add_files git/builtin/add.c:346:7
    #13 0x5651f321f9b2 in cmd_add git/builtin/add.c:565:18
    #14 0x5651f321d327 in run_builtin git/git.c:474:11
    #15 0x5651f321bc9e in handle_builtin git/git.c:729:3
    #16 0x5651f321a792 in run_argv git/git.c:793:4
    #17 0x5651f321a792 in cmd_main git/git.c:928:19
    #18 0x5651f33dde1f in main git/common-main.c:62:11

The issue exists because `size` is an output parameter from
`read_blob_data_from_index`, but it's only modified if
`read_blob_data_from_index` returns non-NULL. The read of `size` when
calling `read_attr_from_buf` unconditionally may read from an
uninitialized value. `read_attr_from_buf` checks that `buf` is non-NULL
before reading from `size`, but by then it's already too late: the
uninitialized read will have happened already. Furthermore, there's no
guarantee that the compiler won't reorder things so that it checks
`size` before checking `!buf`.

Make the call to `read_attr_from_buf` conditional on `buf` being
non-NULL, ensuring that `size` is not read if it's never set.

Signed-off-by: Kyle Lippincott <spectral@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Aug 19, 2024
It was recently reported that concurrent reads and writes may cause the
reftable backend to segfault. The root cause of this is that we do not
properly keep track of reftable readers across reloads.

Suppose that you have a reftable iterator and then decide to reload the
stack while iterating through the iterator. When the stack has been
rewritten since we have created the iterator, then we would end up
discarding a subset of readers that may still be in use by the iterator.
The consequence is that we now try to reference deallocated memory,
which of course segfaults.

One way to trigger this is in t5616, where some background maintenance
jobs have been leaking from one test into another. This leads to stack
traces like the following one:

  + git -c protocol.version=0 -C pc1 fetch --filter=blob:limit=29999 --refetch origin
  AddressSanitizer:DEADLYSIGNAL
  =================================================================
  ==657994==ERROR: AddressSanitizer: SEGV on unknown address 0x7fa0f0ec6089 (pc 0x55f23e52ddf9 bp
0x7ffe7bfa1700 sp 0x7ffe7bfa1700 T0)
  ==657994==The signal is caused by a READ memory access.
      #0 0x55f23e52ddf9 in get_var_int reftable/record.c:29
      #1 0x55f23e53295e in reftable_decode_keylen reftable/record.c:170
      #2 0x55f23e532cc0 in reftable_decode_key reftable/record.c:194
      #3 0x55f23e54e72e in block_iter_next reftable/block.c:398
      #4 0x55f23e5573dc in table_iter_next_in_block reftable/reader.c:240
      #5 0x55f23e5573dc in table_iter_next reftable/reader.c:355
      #6 0x55f23e5573dc in table_iter_next reftable/reader.c:339
      #7 0x55f23e551283 in merged_iter_advance_subiter reftable/merged.c:69
      #8 0x55f23e55169e in merged_iter_next_entry reftable/merged.c:123
      #9 0x55f23e55169e in merged_iter_next_void reftable/merged.c:172
      #10 0x55f23e537625 in reftable_iterator_next_ref reftable/generic.c:175
      #11 0x55f23e2cf9c6 in reftable_ref_iterator_advance refs/reftable-backend.c:464
      #12 0x55f23e2d996e in ref_iterator_advance refs/iterator.c:13
      #13 0x55f23e2d996e in do_for_each_ref_iterator refs/iterator.c:452
      #14 0x55f23dca6767 in get_ref_map builtin/fetch.c:623
      #15 0x55f23dca6767 in do_fetch builtin/fetch.c:1659
      #16 0x55f23dca6767 in fetch_one builtin/fetch.c:2133
      #17 0x55f23dca6767 in cmd_fetch builtin/fetch.c:2432
      #18 0x55f23dba7764 in run_builtin git.c:484
      #19 0x55f23dba7764 in handle_builtin git.c:741
      #20 0x55f23dbab61e in run_argv git.c:805
      #21 0x55f23dbab61e in cmd_main git.c:1000
      #22 0x55f23dba4781 in main common-main.c:64
      #23 0x7fa0f063fc89 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
      #24 0x7fa0f063fd44 in __libc_start_main_impl ../csu/libc-start.c:360
      #25 0x55f23dba6ad0 in _start (git+0xadfad0) (BuildId: 803b2b7f59beb03d7849fb8294a8e2145dd4aa27)

While it is somewhat awkward that the maintenance processes survive
tests in the first place, it is totally expected that reftables should
work alright with concurrent writers. Seemingly they don't.

The only underlying resource that we need to care about in this context
is the reftable reader, which is responsible for reading a single table
from disk. These readers get discarded immediately (unless reused) when
calling `reftable_stack_reload()`, which is wrong. We can only close
them once we know that there are no iterators using them anymore.

Prepare for a fix by converting the reftable readers to be refcounted.

Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Aug 22, 2024
It was recently reported that concurrent reads and writes may cause the
reftable backend to segfault. The root cause of this is that we do not
properly keep track of reftable readers across reloads.

Suppose that you have a reftable iterator and then decide to reload the
stack while iterating through the iterator. When the stack has been
rewritten since we have created the iterator, then we would end up
discarding a subset of readers that may still be in use by the iterator.
The consequence is that we now try to reference deallocated memory,
which of course segfaults.

One way to trigger this is in t5616, where some background maintenance
jobs have been leaking from one test into another. This leads to stack
traces like the following one:

  + git -c protocol.version=0 -C pc1 fetch --filter=blob:limit=29999 --refetch origin
  AddressSanitizer:DEADLYSIGNAL
  =================================================================
  ==657994==ERROR: AddressSanitizer: SEGV on unknown address 0x7fa0f0ec6089 (pc 0x55f23e52ddf9 bp
0x7ffe7bfa1700 sp 0x7ffe7bfa1700 T0)
  ==657994==The signal is caused by a READ memory access.
      #0 0x55f23e52ddf9 in get_var_int reftable/record.c:29
      #1 0x55f23e53295e in reftable_decode_keylen reftable/record.c:170
      #2 0x55f23e532cc0 in reftable_decode_key reftable/record.c:194
      #3 0x55f23e54e72e in block_iter_next reftable/block.c:398
      #4 0x55f23e5573dc in table_iter_next_in_block reftable/reader.c:240
      #5 0x55f23e5573dc in table_iter_next reftable/reader.c:355
      #6 0x55f23e5573dc in table_iter_next reftable/reader.c:339
      #7 0x55f23e551283 in merged_iter_advance_subiter reftable/merged.c:69
      #8 0x55f23e55169e in merged_iter_next_entry reftable/merged.c:123
      #9 0x55f23e55169e in merged_iter_next_void reftable/merged.c:172
      #10 0x55f23e537625 in reftable_iterator_next_ref reftable/generic.c:175
      #11 0x55f23e2cf9c6 in reftable_ref_iterator_advance refs/reftable-backend.c:464
      #12 0x55f23e2d996e in ref_iterator_advance refs/iterator.c:13
      #13 0x55f23e2d996e in do_for_each_ref_iterator refs/iterator.c:452
      #14 0x55f23dca6767 in get_ref_map builtin/fetch.c:623
      #15 0x55f23dca6767 in do_fetch builtin/fetch.c:1659
      #16 0x55f23dca6767 in fetch_one builtin/fetch.c:2133
      #17 0x55f23dca6767 in cmd_fetch builtin/fetch.c:2432
      #18 0x55f23dba7764 in run_builtin git.c:484
      #19 0x55f23dba7764 in handle_builtin git.c:741
      #20 0x55f23dbab61e in run_argv git.c:805
      #21 0x55f23dbab61e in cmd_main git.c:1000
      #22 0x55f23dba4781 in main common-main.c:64
      #23 0x7fa0f063fc89 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
      #24 0x7fa0f063fd44 in __libc_start_main_impl ../csu/libc-start.c:360
      #25 0x55f23dba6ad0 in _start (git+0xadfad0) (BuildId: 803b2b7f59beb03d7849fb8294a8e2145dd4aa27)

While it is somewhat awkward that the maintenance processes survive
tests in the first place, it is totally expected that reftables should
work alright with concurrent writers. Seemingly they don't.

The only underlying resource that we need to care about in this context
is the reftable reader, which is responsible for reading a single table
from disk. These readers get discarded immediately (unless reused) when
calling `reftable_stack_reload()`, which is wrong. We can only close
them once we know that there are no iterators using them anymore.

Prepare for a fix by converting the reftable readers to be refcounted.

Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Aug 23, 2024
It was recently reported that concurrent reads and writes may cause the
reftable backend to segfault. The root cause of this is that we do not
properly keep track of reftable readers across reloads.

Suppose that you have a reftable iterator and then decide to reload the
stack while iterating through the iterator. When the stack has been
rewritten since we have created the iterator, then we would end up
discarding a subset of readers that may still be in use by the iterator.
The consequence is that we now try to reference deallocated memory,
which of course segfaults.

One way to trigger this is in t5616, where some background maintenance
jobs have been leaking from one test into another. This leads to stack
traces like the following one:

  + git -c protocol.version=0 -C pc1 fetch --filter=blob:limit=29999 --refetch origin
  AddressSanitizer:DEADLYSIGNAL
  =================================================================
  ==657994==ERROR: AddressSanitizer: SEGV on unknown address 0x7fa0f0ec6089 (pc 0x55f23e52ddf9 bp
0x7ffe7bfa1700 sp 0x7ffe7bfa1700 T0)
  ==657994==The signal is caused by a READ memory access.
      #0 0x55f23e52ddf9 in get_var_int reftable/record.c:29
      #1 0x55f23e53295e in reftable_decode_keylen reftable/record.c:170
      #2 0x55f23e532cc0 in reftable_decode_key reftable/record.c:194
      #3 0x55f23e54e72e in block_iter_next reftable/block.c:398
      #4 0x55f23e5573dc in table_iter_next_in_block reftable/reader.c:240
      #5 0x55f23e5573dc in table_iter_next reftable/reader.c:355
      #6 0x55f23e5573dc in table_iter_next reftable/reader.c:339
      #7 0x55f23e551283 in merged_iter_advance_subiter reftable/merged.c:69
      #8 0x55f23e55169e in merged_iter_next_entry reftable/merged.c:123
      #9 0x55f23e55169e in merged_iter_next_void reftable/merged.c:172
      #10 0x55f23e537625 in reftable_iterator_next_ref reftable/generic.c:175
      #11 0x55f23e2cf9c6 in reftable_ref_iterator_advance refs/reftable-backend.c:464
      #12 0x55f23e2d996e in ref_iterator_advance refs/iterator.c:13
      #13 0x55f23e2d996e in do_for_each_ref_iterator refs/iterator.c:452
      #14 0x55f23dca6767 in get_ref_map builtin/fetch.c:623
      #15 0x55f23dca6767 in do_fetch builtin/fetch.c:1659
      #16 0x55f23dca6767 in fetch_one builtin/fetch.c:2133
      #17 0x55f23dca6767 in cmd_fetch builtin/fetch.c:2432
      #18 0x55f23dba7764 in run_builtin git.c:484
      #19 0x55f23dba7764 in handle_builtin git.c:741
      #20 0x55f23dbab61e in run_argv git.c:805
      #21 0x55f23dbab61e in cmd_main git.c:1000
      #22 0x55f23dba4781 in main common-main.c:64
      #23 0x7fa0f063fc89 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
      #24 0x7fa0f063fd44 in __libc_start_main_impl ../csu/libc-start.c:360
      #25 0x55f23dba6ad0 in _start (git+0xadfad0) (BuildId: 803b2b7f59beb03d7849fb8294a8e2145dd4aa27)

While it is somewhat awkward that the maintenance processes survive
tests in the first place, it is totally expected that reftables should
work alright with concurrent writers. Seemingly they don't.

The only underlying resource that we need to care about in this context
is the reftable reader, which is responsible for reading a single table
from disk. These readers get discarded immediately (unless reused) when
calling `reftable_stack_reload()`, which is wrong. We can only close
them once we know that there are no iterators using them anymore.

Prepare for a fix by converting the reftable readers to be refcounted.

Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Aug 27, 2024
gitgitgadget bot pushed a commit that referenced this pull request Sep 25, 2024
gitgitgadget bot pushed a commit that referenced this pull request Oct 5, 2024
The incremental MIDX bitmap work was done prior to 9d4855e
(midx-write: fix leaking buffer, 2024-09-30), and causes test failures
in t5334 in a post-9d4855eef3 world.

The leak looks like:

    Direct leak of 264 byte(s) in 1 object(s) allocated from:
        #0 0x7f6bcd87eaca in calloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:90
        #1 0x55ad1428e8a4 in xcalloc wrapper.c:151
        #2 0x55ad14199e16 in prepare_midx_bitmap_git pack-bitmap.c:742
        #3 0x55ad14199447 in open_midx_bitmap_1 pack-bitmap.c:507
        #4 0x55ad14199cca in open_midx_bitmap pack-bitmap.c:704
        #5 0x55ad14199d44 in open_bitmap pack-bitmap.c:717
        #6 0x55ad14199dc2 in prepare_bitmap_git pack-bitmap.c:733
        #7 0x55ad1419e496 in test_bitmap_walk pack-bitmap.c:2698
        #8 0x55ad14047b0b in cmd_rev_list builtin/rev-list.c:629
        #9 0x55ad13f71cd6 in run_builtin git.c:487
        #10 0x55ad13f72132 in handle_builtin git.c:756
        #11 0x55ad13f72380 in run_argv git.c:826
        #12 0x55ad13f728f4 in cmd_main git.c:961
        #13 0x55ad1407d3ae in main common-main.c:64
        #14 0x7f6bcd5f0c89 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
        #15 0x7f6bcd5f0d44 in __libc_start_main_impl ../csu/libc-start.c:360
        #16 0x55ad13f6ff90 in _start (git+0x1ef90) (BuildId: 3e63cdd415f1d185b21da3035cb48332510dddce)

, and is a result of us not freeing the resources corresponding to the
bitmap's base layer, if one was present.

Rectify that leak by calling the newly-introduced free_bitmap_index()
function on the base layer to ensure that its resources are also freed.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Oct 18, 2024
This one is a little bit more curious. In t6112, we have a test that
exercises the `git rev-list --filter` option with invalid filters. We
execute git-rev-list(1) via `test_must_fail`, which means that we check
for leaks even though Git exits with an error code. This causes the
following leak:

    Direct leak of 27 byte(s) in 1 object(s) allocated from:
        #0 0x5555555e6946 in realloc.part.0 lsan_interceptors.cpp.o
        #1 0x5555558fb4b6 in xrealloc wrapper.c:137:8
        #2 0x5555558b6e06 in strbuf_grow strbuf.c:112:2
        #3 0x5555558b7550 in strbuf_add strbuf.c:311:2
        #4 0x5555557c1a88 in strbuf_addstr strbuf.h:310:2
        #5 0x5555557c1d4c in parse_list_objects_filter list-objects-filter-options.c:261:3
        #6 0x555555885ead in handle_revision_pseudo_opt revision.c:2899:3
        #7 0x555555884e20 in setup_revisions revision.c:3014:11
        #8 0x5555556c4b42 in cmd_rev_list builtin/rev-list.c:588:9
        #9 0x5555555ec5e3 in run_builtin git.c:483:11
        #10 0x5555555eb1e4 in handle_builtin git.c:749:13
        #11 0x5555555ec001 in run_argv git.c:819:4
        #12 0x5555555eaf94 in cmd_main git.c:954:19
        #13 0x5555556fd569 in main common-main.c:64:11
        #14 0x7ffff7ca714d in __libc_start_call_main (.../lib/libc.so.6+0x2a14d)
        #15 0x7ffff7ca7208 in __libc_start_main@GLIBC_2.2.5 (.../libc.so.6+0x2a208)
        #16 0x5555555ad064 in _start (git+0x59064)

This leak is valid, as we call `die()` and do not clean up the memory at
all. But what's curious is that this is the only leak reported, because
we don't clean up any other allocated memory, either, and I have no idea
why the leak sanitizer treats this buffer specially.

In any case, we can work around the leak by shuffling things around a
bit. Instead of calling `gently_parse_list_objects_filter()` and dying
after we have modified the filter spec, we simply do so beforehand. Like
this we don't allocate the buffer in the error case, which makes the
reported leak go away.

It's not pretty, but it manages to make t6112 leak free.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
gitgitgadget bot pushed a commit that referenced this pull request Oct 21, 2024
This one is a little bit more curious. In t6112, we have a test that
exercises the `git rev-list --filter` option with invalid filters. We
execute git-rev-list(1) via `test_must_fail`, which means that we check
for leaks even though Git exits with an error code. This causes the
following leak:

    Direct leak of 27 byte(s) in 1 object(s) allocated from:
        #0 0x5555555e6946 in realloc.part.0 lsan_interceptors.cpp.o
        #1 0x5555558fb4b6 in xrealloc wrapper.c:137:8
        #2 0x5555558b6e06 in strbuf_grow strbuf.c:112:2
        #3 0x5555558b7550 in strbuf_add strbuf.c:311:2
        #4 0x5555557c1a88 in strbuf_addstr strbuf.h:310:2
        #5 0x5555557c1d4c in parse_list_objects_filter list-objects-filter-options.c:261:3
        #6 0x555555885ead in handle_revision_pseudo_opt revision.c:2899:3
        #7 0x555555884e20 in setup_revisions revision.c:3014:11
        #8 0x5555556c4b42 in cmd_rev_list builtin/rev-list.c:588:9
        #9 0x5555555ec5e3 in run_builtin git.c:483:11
        #10 0x5555555eb1e4 in handle_builtin git.c:749:13
        #11 0x5555555ec001 in run_argv git.c:819:4
        #12 0x5555555eaf94 in cmd_main git.c:954:19
        #13 0x5555556fd569 in main common-main.c:64:11
        #14 0x7ffff7ca714d in __libc_start_call_main (.../lib/libc.so.6+0x2a14d)
        #15 0x7ffff7ca7208 in __libc_start_main@GLIBC_2.2.5 (.../libc.so.6+0x2a208)
        #16 0x5555555ad064 in _start (git+0x59064)

This leak is valid, as we call `die()` and do not clean up the memory at
all. But what's curious is that this is the only leak reported, because
we don't clean up any other allocated memory, either, and I have no idea
why the leak sanitizer treats this buffer specially.

In any case, we can work around the leak by shuffling things around a
bit. Instead of calling `gently_parse_list_objects_filter()` and dying
after we have modified the filter spec, we simply do so beforehand. Like
this we don't allocate the buffer in the error case, which makes the
reported leak go away.

It's not pretty, but it manages to make t6112 leak free.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
gitgitgadget bot pushed a commit that referenced this pull request Oct 22, 2024
gitgitgadget bot pushed a commit that referenced this pull request Nov 5, 2024
This one is a little bit more curious. In t6112, we have a test that
exercises the `git rev-list --filter` option with invalid filters. We
execute git-rev-list(1) via `test_must_fail`, which means that we check
for leaks even though Git exits with an error code. This causes the
following leak:

    Direct leak of 27 byte(s) in 1 object(s) allocated from:
        #0 0x5555555e6946 in realloc.part.0 lsan_interceptors.cpp.o
        #1 0x5555558fb4b6 in xrealloc wrapper.c:137:8
        #2 0x5555558b6e06 in strbuf_grow strbuf.c:112:2
        #3 0x5555558b7550 in strbuf_add strbuf.c:311:2
        #4 0x5555557c1a88 in strbuf_addstr strbuf.h:310:2
        #5 0x5555557c1d4c in parse_list_objects_filter list-objects-filter-options.c:261:3
        #6 0x555555885ead in handle_revision_pseudo_opt revision.c:2899:3
        #7 0x555555884e20 in setup_revisions revision.c:3014:11
        #8 0x5555556c4b42 in cmd_rev_list builtin/rev-list.c:588:9
        #9 0x5555555ec5e3 in run_builtin git.c:483:11
        #10 0x5555555eb1e4 in handle_builtin git.c:749:13
        #11 0x5555555ec001 in run_argv git.c:819:4
        #12 0x5555555eaf94 in cmd_main git.c:954:19
        #13 0x5555556fd569 in main common-main.c:64:11
        #14 0x7ffff7ca714d in __libc_start_call_main (.../lib/libc.so.6+0x2a14d)
        #15 0x7ffff7ca7208 in __libc_start_main@GLIBC_2.2.5 (.../libc.so.6+0x2a208)
        #16 0x5555555ad064 in _start (git+0x59064)

This leak is valid, as we call `die()` and do not clean up the memory at
all. But what's curious is that this is the only leak reported, because
we don't clean up any other allocated memory, either, and I have no idea
why the leak sanitizer treats this buffer specially.

In any case, we can work around the leak by shuffling things around a
bit. Instead of calling `gently_parse_list_objects_filter()` and dying
after we have modified the filter spec, we simply do so beforehand. Like
this we don't allocate the buffer in the error case, which makes the
reported leak go away.

It's not pretty, but it manages to make t6112 leak free.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Nov 28, 2024
gitgitgadget bot pushed a commit that referenced this pull request Dec 28, 2024
gitgitgadget bot pushed a commit that referenced this pull request Dec 30, 2024
In 1b9e9be (csum-file.c: use unsafe SHA-1 implementation when
available, 2024-09-26) we have converted our `struct hashfile` to use
the unsafe SHA1 backend, which results in a significant speedup. One
needs to be careful with how to use that structure now though because
callers need to consistently use either the safe or unsafe variants of
SHA1, as otherwise one can easily trigger corruption.

As it turns out, we have one inconsistent usage in our tree because we
directly initialize `struct hashfile_checkpoint::ctx` with the safe
variant of SHA1, but end up writing to that context with the unsafe
ones. This went unnoticed so far because our CI systems do not exercise
different hash functions for these two backends, and consequently safe
and unsafe variants are equivalent. But when using SHA1DC as safe and
OpenSSL as unsafe backend this leads to a crash an t1050:

    ++ git -c core.compression=0 add large1
    AddressSanitizer:DEADLYSIGNAL
    =================================================================
    ==1367==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000040 (pc 0x7ffff7a01a99 bp 0x507000000db0 sp 0x7fffffff5690 T0)
    ==1367==The signal is caused by a READ memory access.
    ==1367==Hint: address points to the zero page.
        #0 0x7ffff7a01a99 in EVP_MD_CTX_copy_ex (/nix/store/h1ydpxkw9qhjdxjpic1pdc2nirggyy6f-openssl-3.3.2/lib/libcrypto.so.3+0x201a99) (BuildId: 41746a580d39075fc85e8c8065b6c07fb34e97d4)
        #1 0x555555ddde56 in openssl_SHA1_Clone ../sha1/openssl.h:40:2
        #2 0x555555dce2fc in git_hash_sha1_clone_unsafe ../object-file.c:123:2
        #3 0x555555c2d5f8 in hashfile_checkpoint ../csum-file.c:211:2
        #4 0x555555b9905d in deflate_blob_to_pack ../bulk-checkin.c:286:4
        #5 0x555555b98ae9 in index_blob_bulk_checkin ../bulk-checkin.c:362:15
        #6 0x555555ddab62 in index_blob_stream ../object-file.c:2756:9
        #7 0x555555dda420 in index_fd ../object-file.c:2778:9
        #8 0x555555ddad76 in index_path ../object-file.c:2796:7
        #9 0x555555e947f3 in add_to_index ../read-cache.c:771:7
        #10 0x555555e954a4 in add_file_to_index ../read-cache.c:804:9
        #11 0x5555558b5c39 in add_files ../builtin/add.c:355:7
        #12 0x5555558b412e in cmd_add ../builtin/add.c:578:18
        #13 0x555555b1f493 in run_builtin ../git.c:480:11
        #14 0x555555b1bfef in handle_builtin ../git.c:740:9
        #15 0x555555b1e6f4 in run_argv ../git.c:807:4
        #16 0x555555b1b87a in cmd_main ../git.c:947:19
        #17 0x5555561649e6 in main ../common-main.c:64:11
        #18 0x7ffff742a1fb in __libc_start_call_main (/nix/store/65h17wjrrlsj2rj540igylrx7fqcd6vq-glibc-2.40-36/lib/libc.so.6+0x2a1fb) (BuildId: bf320110569c8ec2425e9a0c5e4eb7e97f1fb6e4)
        #19 0x7ffff742a2b8 in __libc_start_main@GLIBC_2.2.5 (/nix/store/65h17wjrrlsj2rj540igylrx7fqcd6vq-glibc-2.40-36/lib/libc.so.6+0x2a2b8) (BuildId: bf320110569c8ec2425e9a0c5e4eb7e97f1fb6e4)
        #20 0x555555772c84 in _start (git+0x21ec84)

    ==1367==Register values:
    rax = 0x0000511000001080  rbx = 0x0000000000000000  rcx = 0x000000000000000c  rdx = 0x0000000000000000
    rdi = 0x0000000000000000  rsi = 0x0000507000000db0  rbp = 0x0000507000000db0  rsp = 0x00007fffffff5690
     r8 = 0x0000000000000000   r9 = 0x0000000000000000  r10 = 0x0000000000000000  r11 = 0x00007ffff7a01a30
    r12 = 0x0000000000000000  r13 = 0x00007fffffff6b38  r14 = 0x00007ffff7ffd000  r15 = 0x00005555563b9910
    AddressSanitizer can not provide additional info.
    SUMMARY: AddressSanitizer: SEGV (/nix/store/h1ydpxkw9qhjdxjpic1pdc2nirggyy6f-openssl-3.3.2/lib/libcrypto.so.3+0x201a99) (BuildId: 41746a580d39075fc85e8c8065b6c07fb34e97d4) in EVP_MD_CTX_copy_ex
    ==1367==ABORTING
    ./test-lib.sh: line 1023:  1367 Aborted                 git $config add large1
    error: last command exited with $?=134
    not ok 4 - add with -c core.compression=0

Fix the issue by using the unsafe variant instead.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
gitgitgadget bot pushed a commit that referenced this pull request Dec 30, 2024
Same as with the preceding commit, git-fast-import(1) is using the safe
variant to initialize a hashfile checkpoint. This leads to a segfault
when passing the checkpoint into the hashfile subsystem because it would
use the unsafe variants instead:

    ++ git --git-dir=R/.git fast-import --big-file-threshold=1
    AddressSanitizer:DEADLYSIGNAL
    =================================================================
    ==577126==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000040 (pc 0x7ffff7a01a99 bp 0x5070000009c0 sp 0x7fffffff5b30 T0)
    ==577126==The signal is caused by a READ memory access.
    ==577126==Hint: address points to the zero page.
        #0 0x7ffff7a01a99 in EVP_MD_CTX_copy_ex (/nix/store/h1ydpxkw9qhjdxjpic1pdc2nirggyy6f-openssl-3.3.2/lib/libcrypto.so.3+0x201a99) (BuildId: 41746a580d39075fc85e8c8065b6c07fb34e97d4)
        #1 0x555555ddde56 in openssl_SHA1_Clone ../sha1/openssl.h:40:2
        #2 0x555555dce2fc in git_hash_sha1_clone_unsafe ../object-file.c:123:2
        #3 0x555555c2d5f8 in hashfile_checkpoint ../csum-file.c:211:2
        #4 0x5555559647d1 in stream_blob ../builtin/fast-import.c:1110:2
        #5 0x55555596247b in parse_and_store_blob ../builtin/fast-import.c:2031:3
        #6 0x555555967f91 in file_change_m ../builtin/fast-import.c:2408:5
        #7 0x55555595d8a2 in parse_new_commit ../builtin/fast-import.c:2768:4
        #8 0x55555595bb7a in cmd_fast_import ../builtin/fast-import.c:3614:4
        #9 0x555555b1f493 in run_builtin ../git.c:480:11
        #10 0x555555b1bfef in handle_builtin ../git.c:740:9
        #11 0x555555b1e6f4 in run_argv ../git.c:807:4
        #12 0x555555b1b87a in cmd_main ../git.c:947:19
        #13 0x5555561649e6 in main ../common-main.c:64:11
        #14 0x7ffff742a1fb in __libc_start_call_main (/nix/store/65h17wjrrlsj2rj540igylrx7fqcd6vq-glibc-2.40-36/lib/libc.so.6+0x2a1fb) (BuildId: bf320110569c8ec2425e9a0c5e4eb7e97f1fb6e4)
        #15 0x7ffff742a2b8 in __libc_start_main@GLIBC_2.2.5 (/nix/store/65h17wjrrlsj2rj540igylrx7fqcd6vq-glibc-2.40-36/lib/libc.so.6+0x2a2b8) (BuildId: bf320110569c8ec2425e9a0c5e4eb7e97f1fb6e4)
        #16 0x555555772c84 in _start (git+0x21ec84)

    ==577126==Register values:
    rax = 0x0000511000000cc0  rbx = 0x0000000000000000  rcx = 0x000000000000000c  rdx = 0x0000000000000000
    rdi = 0x0000000000000000  rsi = 0x00005070000009c0  rbp = 0x00005070000009c0  rsp = 0x00007fffffff5b30
     r8 = 0x0000000000000000   r9 = 0x0000000000000000  r10 = 0x0000000000000000  r11 = 0x00007ffff7a01a30
    r12 = 0x0000000000000000  r13 = 0x00007fffffff6b60  r14 = 0x00007ffff7ffd000  r15 = 0x00005555563b9910
    AddressSanitizer can not provide additional info.
    SUMMARY: AddressSanitizer: SEGV (/nix/store/h1ydpxkw9qhjdxjpic1pdc2nirggyy6f-openssl-3.3.2/lib/libcrypto.so.3+0x201a99) (BuildId: 41746a580d39075fc85e8c8065b6c07fb34e97d4) in EVP_MD_CTX_copy_ex
    ==577126==ABORTING
    ./test-lib.sh: line 1039: 577126 Aborted                 git --git-dir=R/.git fast-import --big-file-threshold=1 < input
    error: last command exited with $?=134
    not ok 167 - R: blob bigger than threshold

The segfault is only exposed in case the unsafe and safe backends are
different from one another.

Fix the issue by initializing the context with the unsafe SHA1 variant.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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2 participants