mv: strip setuid/setgid when the cross-device copy cannot preserve ownership - #13675
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sylvestre wants to merge 1 commit into
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mv: strip setuid/setgid when the cross-device copy cannot preserve ownership#13675sylvestre wants to merge 1 commit into
sylvestre wants to merge 1 commit into
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…nership When rename(2) returns EXDEV, mv copies the file and then re-applies the source mode, including setuid and setgid. The chown back to the original owner is best-effort and silently ignored, so an unprivileged user moving a root-owned setuid file across a filesystem boundary ended up owning a file that still carried the bits. preserve_ownership now reports whether the destination ended up with the source's uid and gid, and the single-file fallback masks 0o6000 out of the applied mode when it did not. GNU mv does the same, and uutils cp already does (cp.rs, 'GNU cp strips setuid (04000) and setgid (02000) when...'). Measured in a user namespace with two tmpfs mounts, unprivileged uid moving root-owned files: before: f6755 -> mode=6755, f4755 -> 4755, f2755 -> 2755 (owner mover) after : f6755 -> mode=755, f4755 -> 755, f2755 -> 755 GNU : f6755 -> mode=755, f4755 -> 755, f2755 -> 755 When ownership is preserved the bits survive, matching GNU. The directory recursion path already matched GNU and is unchanged. Reported by zerodaybugs via GHSA-6c4j-6pgg-xgg8.
Merging this PR will improve performance by 22.59%
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| Mode | Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|---|
| ⚡ | Simulation | df_with_path |
699.4 µs | 570.5 µs | +22.59% |
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Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.
Comparing sylvestre:mv-strip-setuid-when-chown-fails (c5dc2b7) with main (fc2dfd6)
Footnotes
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46 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. ↩
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When rename(2) returns EXDEV, mv copies the file and then re-applies the source mode, including setuid and setgid. The chown back to the original owner is best-effort and silently ignored, so an unprivileged user moving a root-owned setuid file across a filesystem boundary ended up owning a file that still carried the bits.
preserve_ownership now reports whether the destination ended up with the source's uid and gid, and the single-file fallback masks 0o6000 out of the applied mode when it did not. GNU mv does the same, and uutils cp already does (cp.rs, 'GNU cp strips setuid (04000) and setgid (02000) when...').