fix: strip S_ISGID in chmod() for non-group-member users#363
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fix: strip S_ISGID in chmod() for non-group-member users#363toddr-bot wants to merge 1 commit intocpan-authors:mainfrom
toddr-bot wants to merge 1 commit intocpan-authors:mainfrom
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POSIX chmod(2) silently clears the set-group-ID bit when the calling process is not privileged and is not a member of the file's group. MockFile was allowing S_ISGID unconditionally, which could mask permission bugs in code that relies on this kernel behavior. Also adds S_ISUID/S_ISGID constants and tests for the SGID stripping, SUID preservation, and non-owner EPERM enforcement. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
chmod(2)silently clears the set-group-ID bit when a non-root caller is not a member of the file's group — MockFile was not enforcing thisS_ISUIDandS_ISGIDconstants alongside existingS_IF*definitionsWhy
Same class of POSIX compliance gap as the recent chown/utime/glob permission fixes. Code relying on the kernel's SGID stripping behavior could pass tests under MockFile but fail on real filesystems.
How
After computing the new permission bits in
__chmod, checks whether the mock user is non-root and not in the file's group — if so, masks outS_ISGIDbefore applying.Testing
prove -l t/chmod.t— 3 new subtests (9 assertions) all passfh-ref-leak.tfailure (GH Spooky action-at-a-distance #179)🤖 Generated with Claude Code
Quality Report
Changes: 2 files changed, 119 insertions(+), 2 deletions(-)
Code scan: clean
Tests: failed (4 Failed, 94 test)
Branch hygiene: clean
Generated by Kōan post-mission quality pipeline