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 --- NEWS | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'NEWS') diff --git a/NEWS b/NEWS index b1ae1c31ca..2fe0396b2d 100644 --- a/NEWS +++ b/NEWS @@ -35,6 +35,11 @@ Deprecated and removed features, and other changes affecting compatibility: * The big-endian ARC port (arceb-linux-gnu) has been removed. +* The abort is now async-signal-safe and its implementation makes longjmp + from the SIGABRT handler always abort if set up with setjmp. Use sigsetjmp + to keep the old behavior, where the handler does not stop the process + execution. + Changes to build and runtime requirements: [Add changes to build and runtime requirements here] -- cgit v1.2.3