tmpfs: Clear security.capability xattr on write#13112
Merged
copybara-service[bot] merged 2 commits intomasterfrom May 7, 2026
Merged
tmpfs: Clear security.capability xattr on write#13112copybara-service[bot] merged 2 commits intomasterfrom
copybara-service[bot] merged 2 commits intomasterfrom
Conversation
When a non-privileged user writes to a file on tmpfs, Linux clears both the setuid/setgid mode bits and the security.capability xattr via file_remove_privs. The mode bit clearing was already implemented through ClearSUIDAndSGID, but the xattr removal was missing, so file capabilities survived content replacement. An unprivileged user could overwrite a capability-bearing binary and execute it with the retained privileges. Fixes #13063
copybara-service
Bot
force-pushed
the
test/cl911628845
branch
4 times, most recently
from
a7f6e0d to
b45941b
Compare
PiperOrigin-RevId: 912037144
copybara-service
Bot
force-pushed
the
test/cl911628845
branch
from
b45941b to
d4d9d66
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
tmpfs: Clear security.capability xattr on write
When a non-privileged user writes to a file on tmpfs, Linux clears both the setuid/setgid mode bits and the
security.capabilityxattr viafile_remove_privs. The mode bit clearing was already implemented throughClearSUIDAndSGIDin the pwrite path, but the xattr removal was missing, so file capabilities survived content replacement. An unprivileged user could overwrite a capability-bearing binary and execute it with the retained privileges.The fix adds a
KillPrivmethod onSimpleExtendedAttributesthat removessecurity.capabilitywithout permission checks (matching Linux'scap_inode_killpriv, where the kernel is the actor), and calls it from the tmpfs pwrite path alongside the existingClearSUIDAndSGID.The gofer filesystem is not affected because it explicitly blocks
security.*xattr writes to the host filesystem.Fixes #13063
FUTURE_COPYBARA_INTEGRATE_REVIEW=#13072 from shayonj:fix-cap-survive-write 72063bf