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commitc5efa393d8upstream. The new signal_scoping_thread_setuid tests check that the libc's setuid() function works as expected even when a thread is sandboxed with scoped signal restrictions. Before the signal scoping fix, this test would have failed with the setuid() call: [pid 65] getpid() = 65 [pid 65] tgkill(65, 66, SIGRT_1) = -1 EPERM (Operation not permitted) [pid 65] futex(0x40a66cdc, FUTEX_WAKE_PRIVATE, 1) = 0 [pid 65] setuid(1001) = 0 After the fix, tgkill(2) is successfully leveraged to synchronize credentials update across threads: [pid 65] getpid() = 65 [pid 65] tgkill(65, 66, SIGRT_1) = 0 [pid 66] <... read resumed>0x40a65eb7, 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) [pid 66] --- SIGRT_1 {si_signo=SIGRT_1, si_code=SI_TKILL, si_pid=65, si_uid=1000} --- [pid 66] getpid() = 65 [pid 66] setuid(1001) = 0 [pid 66] futex(0x40a66cdc, FUTEX_WAKE_PRIVATE, 1) = 0 [pid 66] rt_sigreturn({mask=[]}) = 0 [pid 66] read(3, <unfinished ...> [pid 65] setuid(1001) = 0 Test coverage for security/landlock is 92.9% of 1137 lines according to gcc/gcov-14. Fixes:c899496501("selftests/landlock: Test signal scoping for threads") Cc: Günther Noack <gnoack@google.com> Cc: Tahera Fahimi <fahimitahera@gmail.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20250318161443.279194-8-mic@digikod.net [mic: Update test coverage] Signed-off-by: Mickaël Salaün <mic@digikod.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>