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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>
140 lines
4.3 KiB
C
140 lines
4.3 KiB
C
/* fork - create a child process.
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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 <fork.h>
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#include <libio/libioP.h>
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#include <ldsodefs.h>
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#include <malloc/malloc-internal.h>
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#include <nss/nss_database.h>
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#include <register-atfork.h>
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#include <stdio-lock.h>
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#include <sys/single_threaded.h>
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#include <unwind-link.h>
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static void
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fresetlockfiles (void)
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{
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_IO_ITER i;
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for (i = _IO_iter_begin(); i != _IO_iter_end(); i = _IO_iter_next(i))
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if ((_IO_iter_file (i)->_flags & _IO_USER_LOCK) == 0)
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_IO_lock_init (*((_IO_lock_t *) _IO_iter_file(i)->_lock));
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}
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pid_t
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__libc_fork (void)
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{
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/* Determine if we are running multiple threads. We skip some fork
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handlers in the single-thread case, to make fork safer to use in
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signal handlers. Although POSIX has dropped async-signal-safe
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requirement for fork (Austin Group tracker issue #62) this is
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best effort to make is async-signal-safe at least for single-thread
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case. */
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bool multiple_threads = !SINGLE_THREAD_P;
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uint64_t lastrun;
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lastrun = __run_prefork_handlers (multiple_threads);
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struct nss_database_data nss_database_data;
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/* If we are not running multiple threads, we do not have to
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preserve lock state. If fork runs from a signal handler, only
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async-signal-safe functions can be used in the child. These data
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structures are only used by unsafe functions, so their state does
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not matter if fork was called from a signal handler. */
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if (multiple_threads)
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{
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call_function_static_weak (__nss_database_fork_prepare_parent,
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&nss_database_data);
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_IO_list_lock ();
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/* Acquire malloc locks. This needs to come last because fork
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handlers may use malloc, and the libio list lock has an
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indirect malloc dependency as well (via the getdelim
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function). */
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call_function_static_weak (__malloc_fork_lock_parent);
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}
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pid_t pid = _Fork ();
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if (pid == 0)
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{
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fork_system_setup ();
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/* Reset the lock state in the multi-threaded case. */
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if (multiple_threads)
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{
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__libc_unwind_link_after_fork ();
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fork_system_setup_after_fork ();
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call_function_static_weak (__abort_fork_reset_child);
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/* Release malloc locks. */
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call_function_static_weak (__malloc_fork_unlock_child);
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/* Reset the file list. These are recursive mutexes. */
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fresetlockfiles ();
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/* Reset locks in the I/O code. */
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_IO_list_resetlock ();
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call_function_static_weak (__nss_database_fork_subprocess,
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&nss_database_data);
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}
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/* Reset the lock the dynamic loader uses to protect its data. */
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__rtld_lock_initialize (GL(dl_load_lock));
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/* Reset the lock protecting dynamic TLS related data. */
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__rtld_lock_initialize (GL(dl_load_tls_lock));
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reclaim_stacks ();
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/* Run the handlers registered for the child. */
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__run_postfork_handlers (atfork_run_child, multiple_threads, lastrun);
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}
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else
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{
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/* If _Fork failed, preserve its errno value. */
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int save_errno = errno;
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/* Release acquired locks in the multi-threaded case. */
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if (multiple_threads)
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{
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/* Release malloc locks, parent process variant. */
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call_function_static_weak (__malloc_fork_unlock_parent);
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/* We execute this even if the 'fork' call failed. */
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_IO_list_unlock ();
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}
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/* Run the handlers registered for the parent. */
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__run_postfork_handlers (atfork_run_parent, multiple_threads, lastrun);
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if (pid < 0)
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__set_errno (save_errno);
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}
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return pid;
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}
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weak_alias (__libc_fork, __fork)
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libc_hidden_def (__fork)
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weak_alias (__libc_fork, fork)
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