sighook: Don't forget to reset list->tail on the last sigpop()

This was causing a UAF if we ever unregistered the last hook for a
signal and then re-registered one.

Fixes: 75b7f70 ("sighook: Make sigunhook() O(1)")

1 files changed, 2 insertions, 0 deletions

diff --git a/src/sighook.c b/src/sighook.c
index 4356fdb..0cc81fa 100644
--- a/src/sighook.c
+++ b/src/sighook.c
@@ -291,6 +291,8 @@ static void sigpop(struct siglist *list, struct sighook *hook) {
 	rcu_update(hook->self, next);
 	if (next) {
 		next->self = hook->self;
+	} else {
+		list->tail = &list->head;
 	}
 }