From d40ac01cbbc66e6d9dbd8e3485605c63b2178251 Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Thu, 3 Oct 2024 15:41:10 -0300 Subject: stdlib: Make abort/_Exit AS-safe (BZ 26275) 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 --- sysdeps/unix/sysv/linux/internal-signals.h | 9 +++++++++ sysdeps/unix/sysv/linux/internal-sigset.h | 2 +- sysdeps/unix/sysv/linux/spawni.c | 8 ++++++-- 3 files changed, 16 insertions(+), 3 deletions(-) (limited to 'sysdeps/unix/sysv/linux') diff --git a/sysdeps/unix/sysv/linux/internal-signals.h b/sysdeps/unix/sysv/linux/internal-signals.h index a6fae59aaa..6e3a3d7692 100644 --- a/sysdeps/unix/sysv/linux/internal-signals.h +++ b/sysdeps/unix/sysv/linux/internal-signals.h @@ -90,6 +90,15 @@ internal_signal_restore_set (const internal_sigset_t *set) __NSIG_BYTES); } +static inline void +internal_signal_unblock_signal (int sig) +{ + internal_sigset_t set; + internal_sigemptyset (&set); + internal_sigaddset (&set, sig); + INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_UNBLOCK, &set, NULL, + __NSIG_BYTES); +} /* It is used on timer_create code directly on sigwaitinfo call, so it can not use the internal_sigset_t definitions. */ diff --git a/sysdeps/unix/sysv/linux/internal-sigset.h b/sysdeps/unix/sysv/linux/internal-sigset.h index 5d7020b42d..4b19affd75 100644 --- a/sysdeps/unix/sysv/linux/internal-sigset.h +++ b/sysdeps/unix/sysv/linux/internal-sigset.h @@ -21,7 +21,7 @@ #include -typedef struct +typedef struct _internal_sigset_t { unsigned long int __val[__NSIG_WORDS]; } internal_sigset_t; diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c index f57e92815e..1edf62c6d7 100644 --- a/sysdeps/unix/sysv/linux/spawni.c +++ b/sysdeps/unix/sysv/linux/spawni.c @@ -383,7 +383,11 @@ __spawnix (int *pid, const char *file, args.pidfd = 0; args.xflags = xflags; - internal_signal_block_all (&args.oldmask); + /* Avoid the potential issues if caller sets a SIG_IGN for SIGABRT, calls + abort, and another thread issues posix_spawn just after the sigaction + returns. With default options (not setting POSIX_SPAWN_SETSIGDEF), the + process can still see SIG_DFL for SIGABRT, where it should be SIG_IGN. */ + __abort_lock_rdlock (&args.oldmask); /* The clone flags used will create a new child that will run in the same memory space (CLONE_VM) and the execution of calling thread will be @@ -474,7 +478,7 @@ __spawnix (int *pid, const char *file, if ((ec == 0) && (pid != NULL)) *pid = use_pidfd ? args.pidfd : new_pid; - internal_signal_restore_set (&args.oldmask); + __abort_lock_unlock (&args.oldmask); __pthread_setcancelstate (state, NULL); -- cgit 1.4.1