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d40ac01cbb
The recursive lock used on abort does not synchronize with a new process
creation (either by fork-like interfaces or posix_spawn ones), nor it
is reinitialized after fork().
Also, the SIGABRT unblock before raise() shows another race condition,
where a fork or posix_spawn() call by another thread, just after the
recursive lock release and before the SIGABRT signal, might create
programs with a non-expected signal mask. With the default option
(without POSIX_SPAWN_SETSIGDEF), the process can see SIG_DFL for
SIGABRT, where it should be SIG_IGN.
To fix the AS-safe, raise() does not change the process signal mask,
and an AS-safe lock is used if a SIGABRT is installed or the process
is blocked or ignored. With the signal mask change removal,
there is no need to use a recursive loc. The lock is also taken on
both _Fork() and posix_spawn(), to avoid the spawn process to see the
abort handler as SIG_DFL.
A read-write lock is used to avoid serialize _Fork and posix_spawn
execution. Both sigaction (SIGABRT) and abort() requires to lock
as writer (since both change the disposition).
The fallback is also simplified: there is no need to use a loop of
ABORT_INSTRUCTION after _exit() (if the syscall does not terminate the
process, the system is broken).
The proposed fix changes how setjmp works on a SIGABRT handler, where
glibc does not save the signal mask. So usage like the below will now
always abort.
static volatile int chk_fail_ok;
static jmp_buf chk_fail_buf;
static void
handler (int sig)
{
if (chk_fail_ok)
{
chk_fail_ok = 0;
longjmp (chk_fail_buf, 1);
}
else
_exit (127);
}
[...]
signal (SIGABRT, handler);
[....]
chk_fail_ok = 1;
if (! setjmp (chk_fail_buf))
{
// Something that can calls abort, like a failed fortify function.
chk_fail_ok = 0;
printf ("FAIL\n");
}
Such cases will need to use sigsetjmp instead.
The _dl_start_profile calls sigaction through _profil, and to avoid
pulling abort() on loader the call is replaced with __libc_sigaction.
Checked on x86_64-linux-gnu and aarch64-linux-gnu.
Reviewed-by: DJ Delorie <dj@redhat.com>
96 lines
2.9 KiB
C
96 lines
2.9 KiB
C
/* Copyright (C) 1991-2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <signal.h>
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#include <internal-signals.h>
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#include <libc-lock.h>
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#include <pthreadP.h>
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#include <unistd.h>
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/* Try to get a machine dependent instruction which will make the
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program crash. This is used in case everything else fails. */
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#include <abort-instr.h>
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#ifndef ABORT_INSTRUCTION
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/* No such instruction is available. */
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# define ABORT_INSTRUCTION
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#endif
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/* Exported variable to locate abort message in core files etc. */
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struct abort_msg_s *__abort_msg;
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libc_hidden_def (__abort_msg)
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/* The lock is used to prevent multiple thread to change the SIGABRT
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to SIG_IGN while abort tries to change to SIG_DFL, and to avoid
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a new process to see a wrong disposition if there is a SIGABRT
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handler installed. */
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__libc_rwlock_define_initialized (static, lock);
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void
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__abort_fork_reset_child (void)
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{
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__libc_rwlock_init (lock);
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}
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void
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__abort_lock_rdlock (internal_sigset_t *set)
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{
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internal_signal_block_all (set);
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__libc_rwlock_rdlock (lock);
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}
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void
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__abort_lock_wrlock (internal_sigset_t *set)
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{
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internal_signal_block_all (set);
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__libc_rwlock_wrlock (lock);
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}
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void
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__abort_lock_unlock (const internal_sigset_t *set)
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{
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__libc_rwlock_unlock (lock);
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internal_signal_restore_set (set);
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}
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/* Cause an abnormal program termination with core-dump. */
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_Noreturn void
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abort (void)
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{
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raise (SIGABRT);
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/* There is a SIGABRT handle installed and it returned, or SIGABRT was
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blocked or ignored. In this case use a AS-safe lock to prevent sigaction
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to change the signal disposition again, set the handle to default
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disposition, and re-raise the signal. Even if POSIX state this step is
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optional, this a QoI by forcing the process termination through the
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signal handler. */
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__abort_lock_wrlock (NULL);
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struct sigaction act = {.sa_handler = SIG_DFL, .sa_flags = 0 };
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__sigfillset (&act.sa_mask);
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__libc_sigaction (SIGABRT, &act, NULL);
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__pthread_raise_internal (SIGABRT);
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internal_signal_unblock_signal (SIGABRT);
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/* This code should be unreachable, try the arch-specific code and the
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syscall fallback. */
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ABORT_INSTRUCTION;
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_exit (127);
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}
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libc_hidden_def (abort)
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