[PATCH] sigaction should clear all signals on SIG_IGN, not just < 32

While rooting aroung in the signal code trying to understand how to fix the
SIG_IGN ploy (set sig handler to SIG_IGN and flood system with high speed
repeating timers) I came across what, I think, is a problem in sigaction()
in that when processing a SIG_IGN request it flushes signals from 1 to
SIGRTMIN and leaves the rest.  Attempt to fix this.

Signed-off-by: George Anzinger <[email protected]>
Cc: Roland McGrath <[email protected]>
Cc: Linus Torvalds <[email protected]>
Signed-off-by: Adrian Bunk <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/signal.h

@@ -94,6 +94,23 @@ static inline int sigfindinword(unsigned long word)
 
 #endif /* __HAVE_ARCH_SIG_BITOPS */
 
+static inline int sigisemptyset(sigset_t *set)
+{
+	extern void _NSIG_WORDS_is_unsupported_size(void);
+	switch (_NSIG_WORDS) {
+	case 4:
+		return (set->sig[3] | set->sig[2] |
+			set->sig[1] | set->sig[0]) == 0;
+	case 2:
+		return (set->sig[1] | set->sig[0]) == 0;
+	case 1:
+		return set->sig[0] == 0;
+	default:
+		_NSIG_WORDS_is_unsupported_size();
+		return 0;
+	}
+}
+
 #define sigmask(sig)	(1UL << ((sig) - 1))
 
 #ifndef __HAVE_ARCH_SIG_SETOPS

kernel/signal.c

@@ -620,6 +620,33 @@ void signal_wake_up(struct task_struct *t, int resume)
 		kick_process(t);
 }
 
+/*
+ * Remove signals in mask from the pending set and queue.
+ * Returns 1 if any signals were found.
+ *
+ * All callers must be holding the siglock.
+ *
+ * This version takes a sigset mask and looks at all signals,
+ * not just those in the first mask word.
+ */
+static int rm_from_queue_full(sigset_t *mask, struct sigpending *s)
+{
+	struct sigqueue *q, *n;
+	sigset_t m;
+
+	sigandsets(&m, mask, &s->signal);
+	if (sigisemptyset(&m))
+		return 0;
+
+	signandsets(&s->signal, &s->signal, mask);
+	list_for_each_entry_safe(q, n, &s->list, list) {
+		if (sigismember(mask, q->info.si_signo)) {
+			list_del_init(&q->list);
+			__sigqueue_free(q);
+		}
+	}
+	return 1;
+}
 /*
  * Remove signals in mask from the pending set and queue.
  * Returns 1 if any signals were found.
@@ -2408,6 +2435,7 @@ int
 do_sigaction(int sig, const struct k_sigaction *act, struct k_sigaction *oact)
 {
 	struct k_sigaction *k;
+	sigset_t mask;
 
 	if (!valid_signal(sig) || sig < 1 || (act && sig_kernel_only(sig)))
 		return -EINVAL;
@@ -2455,9 +2483,11 @@ do_sigaction(int sig, const struct k_sigaction *act, struct k_sigaction *oact)
 			*k = *act;
 			sigdelsetmask(&k->sa.sa_mask,
 				      sigmask(SIGKILL) | sigmask(SIGSTOP));
-			rm_from_queue(sigmask(sig), &t->signal->shared_pending);
+			sigemptyset(&mask);
+			sigaddset(&mask, sig);
+			rm_from_queue_full(&mask, &t->signal->shared_pending);
 			do {
-				rm_from_queue(sigmask(sig), &t->pending);
+				rm_from_queue_full(&mask, &t->pending);
 				recalc_sigpending_tsk(t);
 				t = next_thread(t);
 			} while (t != current);