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process capabilities for run / exec are inconsistent when --userns=keep-id is set #9919

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klobukowski opened this issue Apr 1, 2021 · 3 comments · Fixed by #9942
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process capabilities for run / exec are inconsistent when --userns=keep-id is set #9919

klobukowski opened this issue Apr 1, 2021 · 3 comments · Fixed by #9942
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@giuseppe @mheon
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In Progress This issue is actively being worked by the assignee, please do not work on this at this time. kind/bug Categorizes issue or PR as related to a bug. locked - please file new issue/PR Assist humans wanting to comment on an old issue or PR with locked comments.

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@klobukowski
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klobukowski commented Apr 1, 2021 •
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Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind bug

Description

When running a container in rootless mode with --userns=keep-id the capabilities are dropped as expected:

[test@hostname ~]$ id
uid=1003(test) gid=1003(test) groups=1003(test)

[test@hostname ~]$ podman run --userns=keep-id -it  docker.io/library/archlinux:latest /bin/captest
User  credentials uid:1003 euid:1003 suid:1003
Group credentials gid:1003 egid:1003 sgid:1003
Current capabilities: none
securebits flags: none
Attempting direct access to shadow...FAILED (Permission denied)
Attempting to access shadow by child process...FAILED
Child User  credentials uid:1003 euid:1003 suid:1003
Child Group credentials gid:1003 egid:1003 sgid:1003
Child capabilities: none
Child securebits flags: none

However, If I run a container in the background:

[test@hostname ~]$ podman run --userns=keep-id -it  docker.io/library/archlinux:latest /bin/sleep 1000

and exec another command in the same container, the UID seems to be mapped correctly but the capabilities are not dropped by default:

[test@hostname ~]$ podman exec -itl /bin/captest
User  credentials uid:1003 euid:1003 suid:1003
Group credentials gid:1003 egid:1003 sgid:1003
Effective:    00000000, 800405FB
Permitted:    00000000, 800405FB
Inheritable:  00000000, 800405FB
Bounding Set: 00000000, 800405FB
Ambient :     00000000, 800405FB
securebits flags: none
Attempting direct access to shadow...FAILED (Permission denied)
Attempting to access shadow by child process...SUCCESS
Attempting to regain root...SUCCESS - PRIVILEGE ESCALATION POSSIBLE
Child User  credentials uid:0 euid:0 suid:0
Child Group credentials gid:0 egid:0 sgid:0
Child capabilities:
Effective:    00000000, 800405FB
Permitted:    00000000, 800405FB
Inheritable:  00000000, 800405FB
Bounding Set: 00000000, 800405FB
Ambient :     00000000, 800405FB
Child securebits flags: none
Attempting direct access to shadow...SUCCESS

To fix this I need to specify the --user option explicitly even though the UID is already mapped via --userns=keep-id

[test@hostname ~]$ podman exec --user 1003:1003  -itl /bin/captest
User  credentials uid:1003 euid:1003 suid:1003
Group credentials gid:1003 egid:1003 sgid:1003
Current capabilities: none
securebits flags: none
Attempting direct access to shadow...FAILED (Permission denied)
Attempting to access shadow by child process...FAILED
Child User  credentials uid:1003 euid:1003 suid:1003
Child Group credentials gid:1003 egid:1003 sgid:1003
Child capabilities: none
Child securebits flags: none
[

Steps to reproduce the issue:

as above

Describe the results you received:

Process capabilities are different for podman run and podman exec commands.

Describe the results you expected:

podman exec should drop the capabilities for the user process by default if --userns=keep-id was set.

Output of podman version:

Version:      3.1.0
API Version:  3.1.0
Go Version:   go1.16.2
Git Commit:   9f09fb62cba8f44c18eda84db3e72aab3ae76046-dirty
Built:        Wed Mar 31 16:46:48 2021
OS/Arch:      linux/amd64
@openshift-ci-robot openshift-ci-robot added the kind/bug Categorizes issue or PR as related to a bug. label Apr 1, 2021
@rhatdan
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rhatdan commented Apr 5, 2021

@mheon @giuseppe This is pretty serious. Is there any way to know when we are execing into the container, that we are running with a keep-id user namespace?

@mheon
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mheon commented Apr 5, 2021

We don't retain keep-id itself. I suppose we could parse the userns mappings to determine what's going on there?

@mheon
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mheon commented Apr 5, 2021

Found it.

@mheon mheon added the In Progress This issue is actively being worked by the assignee, please do not work on this at this time. label Apr 5, 2021
@mheon mheon mentioned this issue Apr 5, 2021
Merged
mheon added a commit to mheon/libpod that referenced this issue Apr 6, 2021
@mheon
Ensure that --userns=keep-id sets user in config
541252a 
One of the side-effects of the `--userns=keep-id` command is
switching the default user of the container to the UID of the
user running Podman (though this can still be overridden by the
`--user` flag). However, it did this by setting the UID and GID
in the OCI spec, and not by informing Libpod of its intention to
switch users via the `WithUser()` option. Because of this, a lot
of the code that should have triggered when the container ran
with a non-root user was not triggering. In the case of the issue
that this fixed, the code to remove capabilities from non-root
users was not triggering. Adjust the keep-id code to properly
inform Libpod of our intention to use a non-root user to fix
this.

Also, fix an annoying race around short-running exec sessions
where Podman would always print a warning that the exec session
had already stopped.

Fixes containers#9919

Signed-off-by: Matthew Heon <matthew.heon@pm.me>
mheon added a commit to mheon/libpod that referenced this issue Apr 16, 2021
@mheon
Ensure that --userns=keep-id sets user in config
0cbd322 
One of the side-effects of the `--userns=keep-id` command is
switching the default user of the container to the UID of the
user running Podman (though this can still be overridden by the
`--user` flag). However, it did this by setting the UID and GID
in the OCI spec, and not by informing Libpod of its intention to
switch users via the `WithUser()` option. Because of this, a lot
of the code that should have triggered when the container ran
with a non-root user was not triggering. In the case of the issue
that this fixed, the code to remove capabilities from non-root
users was not triggering. Adjust the keep-id code to properly
inform Libpod of our intention to use a non-root user to fix
this.

Also, fix an annoying race around short-running exec sessions
where Podman would always print a warning that the exec session
had already stopped.

Fixes containers#9919

Signed-off-by: Matthew Heon <matthew.heon@pm.me>
jmguzik pushed a commit to jmguzik/podman that referenced this issue Apr 26, 2021
@mheon @jmguzik
Ensure that --userns=keep-id sets user in config
234bf4c 
One of the side-effects of the `--userns=keep-id` command is
switching the default user of the container to the UID of the
user running Podman (though this can still be overridden by the
`--user` flag). However, it did this by setting the UID and GID
in the OCI spec, and not by informing Libpod of its intention to
switch users via the `WithUser()` option. Because of this, a lot
of the code that should have triggered when the container ran
with a non-root user was not triggering. In the case of the issue
that this fixed, the code to remove capabilities from non-root
users was not triggering. Adjust the keep-id code to properly
inform Libpod of our intention to use a non-root user to fix
this.

Also, fix an annoying race around short-running exec sessions
where Podman would always print a warning that the exec session
had already stopped.

Fixes containers#9919

Signed-off-by: Matthew Heon <matthew.heon@pm.me>
@github-actions github-actions bot added the locked - please file new issue/PR Assist humans wanting to comment on an old issue or PR with locked comments. label Sep 22, 2023
@github-actions github-actions bot locked as resolved and limited conversation to collaborators Sep 22, 2023
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@giuseppe giuseppe

@mheon mheon

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In Progress This issue is actively being worked by the assignee, please do not work on this at this time. kind/bug Categorizes issue or PR as related to a bug. locked - please file new issue/PR Assist humans wanting to comment on an old issue or PR with locked comments.
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Ensure that --userns=keep-id sets user in config mheon/libpod
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@giuseppe @rhatdan @klobukowski @mheon @openshift-ci-robot