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nptl: Install SIGSETXID handler with SA_ONSTACK [BZ #27914]

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The signal is sent to all threads, some of which may have switched
to very small stacks.  If they have also installed an alternate
signal stack, SA_ONSTACK makes this work.  The Go runtime needs this:

  runtime: C.setuid/C.setgid smashes Go stack
  <https://github.com/golang/go/issues/9400>

Doing this for SIGCANCEL is less obviously beneficial and needs further
testing.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Florian Weimer 2021-05-27 15:37:35 +02:00
parent 4f26956d5b
commit 76b0c59e33
1 changed files with 5 additions and 2 deletions
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7
nptl/pthread_create.c
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@ -83,9 +83,12 @@ late_init (void)
(void) __libc_sigaction (SIGCANCEL, &sa, NULL);
}
/* Install the handle to change the threads' uid/gid. */
/* Install the handle to change the threads' uid/gid. Use
SA_ONSTACK because the signal may be sent to threads that are
running with custom stacks. (This is less likely for
SIGCANCEL.) */
sa.sa_sigaction = __nptl_setxid_sighandler;
sa.sa_flags = SA_SIGINFO | SA_RESTART;
sa.sa_flags = SA_ONSTACK | SA_SIGINFO | SA_RESTART;
(void) __libc_sigaction (SIGSETXID, &sa, NULL);
/* The parent process might have left the signals blocked. Just in