chmod, chown: check --preserve-root on the directory actually descended into by abendrothj · Pull Request #14972 · uutils/coreutils

abendrothj · 2026-09-30T02:28:17Z

The recursive operand of chmod, chown and chgrp was checked against --preserve-root with its own path lookup, separate from the one the change and the descent used. A rename landing in between could send a -H/-L recursion into "/" after the check had passed.

On Linux, chown/chgrp now also decide on the stat that the operand's descriptor is already verified against. chmod opens the operand, checks that descriptor, and changes its mode through it; it still reopens the directory to descend, like GNU, and only continues if it is the same directory. Under -P this also stops the operand's own mode change from following a symlink swapped in at the directory's name, unless the open itself is refused and chmod goes by path. If the operand can't be opened because it isn't readable yet, the system refuses it (EPERM, as under a macOS sandbox) or this process has no descriptor left, chmod changes its mode by name, as GNU does; other errors are reported.

test_chmod_recursive_descends_only_into_the_directory_it_changed races a thread that re-points the operand, over 200 runs. Without the change it failed 10 of 10 times on Linux and on macOS; with it, it passed every time (30 on Linux, 20 on macOS), in about 0.3 s on Linux. test_chmod_recursive_operand_refused_by_sandbox runs only on macOS, through sandbox-exec. Run on macOS and Linux; FreeBSD, Android and Redox are only cross-checked with clippy.

Closes #14990

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codspeed · 2026-09-30T03:05:31Z

Merging this PR will not alter performance

1 warning, 1 note

⚠️ 124 benchmarks are dominated by system calls

System calls cannot be simulated consistently and are left out of the measure. The reported value understates the real cost. Switch to the Walltime instrument to measure them.

Learn more about system calls

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ℹ️ 1 benchmark has no flamegraph

The flamegraph wasn't generated: most of the time was spent in runtime internals, which would leave nothing useful to analyze.

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✅ 401 untouched benchmarks
⏩ 70 skipped benchmarks¹

_{Comparing abendrothj:chmod-chown-operand-by-fd (683dd8a) with main (4a78f16)}

70 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

github-actions · 2026-09-30T03:14:41Z

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)

abendrothj · 2026-10-01T00:53:35Z

Opened #14990.

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abendrothj · 2026-10-01T02:10:56Z

The SELinux GNU job failed while booting its VM, before any test ran; unrelated to this change.

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abendrothj · 2026-10-07T08:12:13Z

rebased on #15030: the gates here are Redox-only now, like the rest of chmod. with the old ones, chmod wouldn't have built on Hurd/AIX once both were merged (main + this failed Hurd clippy). cross-checked with clippy for Hurd and AIX, not run there. back out of draft once ci is green.

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xtqqczze · 2026-10-18T09:26:12Z

AIX is only cross-checked with clippy (AIX with libc 0.2.189, see #15083).

You should be able to compile for AIX now with libc v0.2.191.

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abendrothj · 2026-10-19T02:32:17Z

Thanks, clippy for powerpc64-ibm-aix passes now. Updated the description.

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sylvestre · 2026-10-25T09:43:35Z

rebased on main's chmod reporting refactor: errors go through report_failure, dropped CannotAccess (same text as CannotStat), and the unreadable-operand test now expects 'cannot read directory' like GNU

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sylvestre · 2026-11-03T12:41:31Z

a bunch of jobs are failing

On Linux, a rename between the path lookup and the descent can no longer slip "/" past --preserve-root under -H or -L.

A rename between the checks can no longer send the mode change or the descent into "/", also under -L.

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Follow-up to 07b66ef (uutils#14972): fall back to the path on any open failure instead of an errno allowlist, and keep only the symlink-operand and unopenable-operand tests.

Follow-up to 07b66ef (uutils#14972): fall back to the path only when permissions keep the operand from opening, instead of an errno allowlist, and drop the tests for -h, sandboxed operands and the descriptor count.

Follow-up to 07b66ef (uutils#14972): fall back to the path only when permissions keep the operand from opening, instead of an errno allowlist.

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abendrothj added 2 commits November 6, 2026 19:46

chown, chgrp: judge --preserve-root on the stat the descent is pinned to

7d95463

On Linux, a rename between the path lookup and the descent can no longer slip "/" past --preserve-root under -H or -L.

chmod: change the -R operand's mode through a descriptor

683dd8a

A rename between the checks can no longer send the mode change or the descent into "/", also under -L.

abendrothj force-pushed the chmod-chown-operand-by-fd branch from f031f8c to 683dd8a Compare November 7, 2026 06:33

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sylvestre merged commit 07b66ef into uutils:main Nov 8, 2026
231 of 232 checks passed

sylvestre mentioned this pull request Nov 8, 2026

chmod: simplify the -R operand's descriptor handling #16294

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Merging this PR will not alter performance

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