Do not attempt to report proc event if NOTE_EXIT has already been received.

This fixes a race condition (specifically with signal events) that could
lead to the kn being re-inserted into the list after it has been destroyed,
which is not something we want to happen.

PR:		kern/58258

1 files changed, 7 insertions, 0 deletions

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index a9e42de..85ee24e 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -280,6 +280,13 @@ filt_proc(struct knote *kn, long hint)
 	}
 
 	/*
+	 * Process will already be reported as gone.
+	 * Do not report anything else, as the knote will be destroyed soon.
+	 */
+	if (kn->kn_status & KN_DETACHED)
+		return (0);
+
+	/*
 	 * process forked, and user wants to track the new process,
 	 * so attach a new knote to it, and immediately report an
 	 * event with the parent's pid.