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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>
119 lines
3.4 KiB
C
119 lines
3.4 KiB
C
/* Special use of signals internally. Linux version.
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Copyright (C) 2014-2024 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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#ifndef __INTERNAL_SIGNALS_H
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# define __INTERNAL_SIGNALS_H
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#include <internal-sigset.h>
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#include <limits.h>
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#include <signal.h>
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#include <sigsetops.h>
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#include <stdbool.h>
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#include <stddef.h>
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#include <sysdep.h>
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/* The signal used for asynchronous cancelation. */
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#define SIGCANCEL __SIGRTMIN
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/* Signal needed for the kernel-supported POSIX timer implementation.
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We can reuse the cancellation signal since we can distinguish
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cancellation from timer expirations. */
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#define SIGTIMER SIGCANCEL
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/* Signal used to implement the setuid et.al. functions. */
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#define SIGSETXID (__SIGRTMIN + 1)
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/* How many signal numbers need to be reserved for libpthread's private uses
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(SIGCANCEL and SIGSETXID). */
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#define RESERVED_SIGRT 2
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/* Return is sig is used internally. */
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static inline bool
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is_internal_signal (int sig)
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{
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return (sig == SIGCANCEL) || (sig == SIGSETXID);
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}
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/* Remove internal glibc signal from the mask. */
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static inline void
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clear_internal_signals (sigset_t *set)
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{
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__sigdelset (set, SIGCANCEL);
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__sigdelset (set, SIGSETXID);
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}
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static const internal_sigset_t sigall_set = {
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.__val = {[0 ... __NSIG_WORDS-1 ] = -1 }
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};
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/* Obtain and change blocked signals, including internal glibc ones. */
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static inline int
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internal_sigprocmask (int how, const internal_sigset_t *set,
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internal_sigset_t *oldset)
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{
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return INTERNAL_SYSCALL_CALL (rt_sigprocmask, how, set, oldset,
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__NSIG_BYTES);
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}
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/* Block all signals, including internal glibc ones. */
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static inline void
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internal_signal_block_all (internal_sigset_t *oset)
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{
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INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_BLOCK, &sigall_set, oset,
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__NSIG_BYTES);
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}
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/* Restore current process signal mask. */
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static inline void
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internal_signal_restore_set (const internal_sigset_t *set)
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{
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INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_SETMASK, set, NULL,
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__NSIG_BYTES);
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}
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static inline void
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internal_signal_unblock_signal (int sig)
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{
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internal_sigset_t set;
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internal_sigemptyset (&set);
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internal_sigaddset (&set, sig);
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INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_UNBLOCK, &set, NULL,
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__NSIG_BYTES);
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}
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/* It is used on timer_create code directly on sigwaitinfo call, so it can not
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use the internal_sigset_t definitions. */
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static const sigset_t sigtimer_set = {
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.__val = { [0] = __sigmask (SIGTIMER),
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[1 ... _SIGSET_NWORDS-1] = 0
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}
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};
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/* Unblock only SIGTIMER. */
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static inline void
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signal_unblock_sigtimer (void)
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{
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INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_UNBLOCK, &sigtimer_set, NULL,
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__NSIG_BYTES);
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}
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#endif
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