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Read root-owned files as an unprivileged user. Pre-31e62c2ebbfd kernels (everything in stable as of 2026-05-14).

The bug
__ptrace_may_access() skips the dumpable check when task->mm == NULL. do_exit() runs exit_mm() before exit_files() — no mm, fds still there. pidfd_getfd(2) succeeds in that window when the caller's uid matches the target's.

Reported by Qualys, fixed by Linus 2026-05-14. Jann Horn flagged the FD-theft shape in October 2020. Six years.

Reproducers, if any, will remain confidential and never be made public, unless done so by the security team.