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 --- include/bits/unistd_ext.h | 3 +++ include/stdlib.h | 7 +++++++ 2 files changed, 10 insertions(+) (limited to 'include') diff --git a/include/bits/unistd_ext.h b/include/bits/unistd_ext.h index 277be05..eeb07ba 100644 --- a/include/bits/unistd_ext.h +++ b/include/bits/unistd_ext.h @@ -3,4 +3,7 @@ #ifndef _ISOMAC extern int __close_range (unsigned int lowfd, unsigned int highfd, int flags); libc_hidden_proto (__close_range); + +extern pid_t __gettid (void); +libc_hidden_proto (__gettid); #endif diff --git a/include/stdlib.h b/include/stdlib.h index 0cab3f5..57f4ab8 100644 --- a/include/stdlib.h +++ b/include/stdlib.h @@ -20,6 +20,7 @@ # include # include +# include extern __typeof (strtol_l) __strtol_l; extern __typeof (strtoul_l) __strtoul_l; @@ -77,6 +78,12 @@ libc_hidden_proto (__isoc23_strtoull_l) # define strtoull_l __isoc23_strtoull_l #endif +extern void __abort_fork_reset_child (void) attribute_hidden; +extern void __abort_lock_rdlock (internal_sigset_t *set) attribute_hidden; +extern void __abort_lock_wrlock (internal_sigset_t *set) attribute_hidden; +extern void __abort_lock_unlock (const internal_sigset_t *set) + attribute_hidden; + libc_hidden_proto (exit) libc_hidden_proto (abort) libc_hidden_proto (getenv) -- cgit v1.1