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Fix clearing set-uid and set-gid bits on a file when replying a write. #13027

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merged 1 commit into from
Feb 3, 2022

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pjd
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@pjd pjd commented Jan 28, 2022

Motivation and Context

POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write, set-uid and set-gid bits
are not removed from the file.

Description

Log a separate TX_SETATTR entry in ZIL that removed set-uid and set-gid bits on first write to a file.

How Has This Been Tested?

The procedure I've used to reproduce the problem is as follows (on FreeBSD):

zpool create -O sync=always tank ada0
touch /tank/foo
chown nobody /tank/foo
chmod 6755 /tank/foo
ls -l /tank/foo
-rwsr-sr-x 1 nobody wheel 0 Jan 27 14:33 /tank/foo
su -m nobody -c 'echo foo > /tank/foo' ; sysctl debug.kdb.panic=1

This writes to the file and panics the kernel. After reboot, without the fix we would have file's content modified, but the set-uid and set-gid bits still set. After the fix, those bits are properly removed.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Performance enhancement (non-breaking change which improves efficiency)
  • Code cleanup (non-breaking change which makes code smaller or more readable)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
  • Documentation (a change to man pages or other documentation)

Checklist:

@problame
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@pjd I mentioned in the e-mail thread that I already had follow-up patches. Sorry that it took so long.
I posted a PR to this branch ( pjd#1 ) that adds

  • fixups for the error code paths (we need to clear setuid bits on partial writes as well)
  • a regression test for the ZTS

@danmcd
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danmcd commented Jan 28, 2022

Please fold in @problame 's additions and/or explain why not to take them? I'd like to port this to illumos but can't until the discussion has settled somewhat here. (And naturally the illumos commit will have appropriate author and co-author attributions to you two.)

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The backport to illumos-gate is much smaller, because we don't have other dmu_tx_commit() calls in our zfs_write, and we don't have the basic suid tests backported yet either.

What I do have, and what I see here, both look good.

@behlendorf behlendorf added the Status: Code Review Needed Ready for review and testing label Feb 2, 2022
@behlendorf
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@pjd would you mind rebasing this commit on the latest master branch and squashing the commits.

POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Signed-off-by:	Pawel Jakub Dawidek <pawel@dawidek.net>
Co-authored-by:	Christian Schwarz <me@cschwarz.com>
@pjd
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pjd commented Feb 2, 2022

@pjd would you mind rebasing this commit on the latest master branch and squashing the commits.

Done.

@behlendorf behlendorf added Status: Accepted Ready to integrate (reviewed, tested) and removed Status: Code Review Needed Ready for review and testing labels Feb 2, 2022
@behlendorf behlendorf merged commit 3d244b4 into openzfs:master Feb 3, 2022
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 10, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 14, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 16, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
@lundman
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lundman commented Feb 17, 2022

Sorry I'm late, my only complaints is that this uses AT_MODE in the shared module/zfs/zfs_vnops.c, there are no AT_ use in the shared files, only ATTR_ - so it feels like ATTR_MODE should have been used.

@behlendorf
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behlendorf commented Feb 17, 2022

Whoops, you're right. Looks like we missed that in the review, mind opening a PR to switch the name so we can get it sorted out.

@lundman
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lundman commented Feb 17, 2022

Yeah will do - I just want to get to the end of the rebase in case there are more :)

tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 17, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
nicman23 pushed a commit to nicman23/zfs that referenced this pull request Aug 22, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
nicman23 pushed a commit to nicman23/zfs that referenced this pull request Aug 22, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
snajpa pushed a commit to vpsfreecz/zfs that referenced this pull request Oct 22, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
snajpa pushed a commit to vpsfreecz/zfs that referenced this pull request Oct 22, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
snajpa pushed a commit to vpsfreecz/zfs that referenced this pull request Oct 23, 2022
POSIX requires that set-uid and set-gid bits to be removed when an
unprivileged user writes to a file and ZFS does that during normal
operation.

The problem arrises when the write is stored in the ZIL and replayed.
During replay we have no access to original credentials of the process
doing the write, so zfs_write() will be performed with the root
credentials. When root is doing the write set-uid and set-gid bits
are not removed from the file.

To correct that, log a separate TX_SETATTR entry that removed those bits
on first write to such file.

Idea from:	Christian Schwarz

Add test for ZIL replay of setuid/setgid clearing.

Improve various edge cases when clearing setid bits:
- The setid bits can be readded during a single write, so make sure to check
  for them on every chunk write.
- Log TX_SETATTR record at most once per transaction group (if the setid bits
  are keep coming back).
- Move zfs_log_setattr() outside of zp->z_acl_lock.

Reviewed-by: Dan McDonald <danmcd@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Christian Schwarz <me@cschwarz.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes openzfs#13027
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5 participants