Fix capability loss uid override#509
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Benchmark results for collatzParameters
SummaryFound 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics. See unchanged results
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Benchmark results for BadBoggleSolver_runParameters
SummaryFound 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics. See unchanged results
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r1viollet
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| // process capability sets. Fully reproducing that needs a non-root process that | ||
| // also holds CAP_SETUID and CAP_SETGID, which is uncommon in CI. | ||
| // | ||
| // How we reproduced this in a privileged container |
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added instructions here are on how to reproduce the issue (as even with LLMs, it was quite painful to do)
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When ddprof runs as a non-root user with file capabilities (e.g.
CAP_IPC_LOCK, CAP_PERFMON), the UID round-trip in open_proc_maps()
and open_proc_comm() permanently destroys all capabilities:
1. fopen("/proc/<pid>/maps") fails (target is non-dumpable)
2. stat() shows file owned by root (st_uid=0)
3. setresuid(0, 0, -1) sets real+effective to 0, saved stays 1000
4. Retry fopen still fails (needs CAP_SYS_PTRACE, not just UID 0)
5. setresuid(1000, 1000, -1) restores UIDs — all nonzero
6. Kernel clears ALL capabilities (Linux cap clearing rule)
7. Worker permanently loses IPC_LOCK + PERFMON → profiling breaks
Guard the UID elevation with `is_root()` so non-root users skip the
elevation attempt entirely, preserving their file capabilities.
Add unit tests covering capability preservation for the fixed path,
including a reproducer for the original bug.
Co-Authored-By: Xavier Roche <[email protected]>
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What does this PR do?
Refer to following PR
I adjusted to allow switching if the file is not a file from a root user.
Motivation
Avoid capability loss.
Refer to original PR
Additional Notes
NA
How to test the change?
Unit tests were added, thank you @xroche