always terminate by SIGABRT when abort is called

Linux makes this surprisingly difficult, but it can be done. the trick
here is using the fact that we control the implementation of sigaction
to prevent changing the disposition of SIGABRT to anything but SIG_DFL
after abort has tried and failed to terminate the process simply by
calling raise(SIGABRT).

1 files changed, 21 insertions, 4 deletions

diff --git a/src/signal/sigaction.c b/src/signal/sigaction.c
index 6eca06f1..79989500 100644
--- a/src/signal/sigaction.c
+++ b/src/signal/sigaction.c
@@ -6,6 +6,11 @@
 #include "libc.h"
 #include "ksigaction.h"
 
+volatile int dummy_lock[1] = { 0 };
+
+__attribute__((__visibility__("hidden")))
+weak_alias(dummy_lock, __abort_lock);
+
 static int unmask_done;
 static unsigned long handler_set[_NSIG/(8*sizeof(long))];
 
@@ -17,6 +22,7 @@ void __get_handler_set(sigset_t *set)
 int __libc_sigaction(int sig, const struct sigaction *restrict sa, struct sigaction *restrict old)
 {
 	struct k_sigaction ksa, ksa_old;
+	unsigned long set[_NSIG/(8*sizeof(long))];
 	if (sa) {
 		if ((uintptr_t)sa->sa_handler > 1UL) {
 			a_or_l(handler_set+(sig-1)/(8*sizeof(long)),
@@ -36,19 +42,30 @@ int __libc_sigaction(int sig, const struct sigaction *restrict sa, struct sigact
 				unmask_done = 1;
 			}
 		}
+		/* Changing the disposition of SIGABRT to anything but
+		 * SIG_DFL requires a lock, so that it cannot be changed
+		 * while abort is terminating the process after simply
+		 * calling raise(SIGABRT) failed to do so. */
+		if (sa->sa_handler != SIG_DFL && sig == SIGABRT) {
+			__block_all_sigs(&set);
+			LOCK(__abort_lock);
+		}
 		ksa.handler = sa->sa_handler;
 		ksa.flags = sa->sa_flags | SA_RESTORER;
 		ksa.restorer = (sa->sa_flags & SA_SIGINFO) ? __restore_rt : __restore;
 		memcpy(&ksa.mask, &sa->sa_mask, sizeof ksa.mask);
 	}
-	if (syscall(SYS_rt_sigaction, sig, sa?&ksa:0, old?&ksa_old:0, sizeof ksa.mask))
-		return -1;
-	if (old) {
+	int r = __syscall(SYS_rt_sigaction, sig, sa?&ksa:0, old?&ksa_old:0, sizeof ksa.mask);
+	if (sig == SIGABRT && sa && sa->sa_handler != SIG_DFL) {
+		UNLOCK(__abort_lock);
+		__restore_sigs(&set);
+	}
+	if (old && !r) {
 		old->sa_handler = ksa_old.handler;
 		old->sa_flags = ksa_old.flags;
 		memcpy(&old->sa_mask, &ksa_old.mask, sizeof ksa_old.mask);
 	}
-	return 0;
+	return __syscall_ret(r);
 }
 
 int __sigaction(int sig, const struct sigaction *restrict sa, struct sigaction *restrict old)