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authorRich Felker <dalias@aerifal.cx>2018-09-01 01:54:44 -0400
committerRich Felker <dalias@aerifal.cx>2018-09-01 02:06:10 -0400
commit9b14ad541068d4f7d0be9bcd1ff4c70090d868d3 (patch)
treeee80fd4be7d6d4a96858e02d76e4b53f038bf35d
parent0b4c92b7acf63529858e7f8a3bb6505cd2b6e962 (diff)
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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).
-rw-r--r--src/exit/abort.c19
-rw-r--r--src/signal/sigaction.c25
2 files changed, 40 insertions, 4 deletions
diff --git a/src/exit/abort.c b/src/exit/abort.c
index ecc0f735..d6bd546b 100644
--- a/src/exit/abort.c
+++ b/src/exit/abort.c
@@ -3,11 +3,30 @@
 #include "syscall.h"
 #include "pthread_impl.h"
 #include "atomic.h"
+#include "libc.h"
+#include "ksigaction.h"
+
+__attribute__((__visibility__("hidden")))
+volatile int __abort_lock[1];
 
 _Noreturn void abort(void)
 {
 	raise(SIGABRT);
+
+	/* If there was a SIGABRT handler installed and it returned, or if
+	 * SIGABRT was blocked or ignored, take an AS-safe lock to prevent
+	 * sigaction from installing a new SIGABRT handler, uninstall any
+	 * handler that may be present, and re-raise the signal to generate
+	 * the default action of abnormal termination. */
 	__block_all_sigs(0);
+	LOCK(__abort_lock);
+	__syscall(SYS_rt_sigaction, SIGABRT,
+		&(struct k_sigaction){.handler = SIG_DFL}, 0, _NSIG/8);
+	__syscall(SYS_tkill, __pthread_self()->tid, SIGABRT);
+	__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
+		&(long[_NSIG/(8*sizeof(long))]){1UL<<(SIGABRT-1)}, 0, _NSIG/8);
+
+	/* Beyond this point should be unreachable. */
 	a_crash();
 	raise(SIGKILL);
 	_Exit(127);
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)