From: Kirill A. Korinsky <kirill@korins.ky>
Subject: event_asr_dispatch: respect error from event_add
To: OpenBSD tech <tech@openbsd.org>
Date: Fri, 14 Jun 2024 21:55:02 +0100

tech@,

I noticed that event_asr_dispatch never checks the return of event_add,
which can lead to a kind of deadlock when an application expects the
callback to fire, but it doesn't fire because asr_run returned error, and it
can't schedule the new attempt.

Here is a suggested diff that sets ar_errno and ar_h_errno and fires the
callback.

diff --git lib/libevent/event.c lib/libevent/event.c
index 26bc37dea76..007564a8b2c 100644
--- lib/libevent/event.c
+++ lib/libevent/event.c
@@ -951,7 +951,12 @@ event_asr_dispatch(int fd __attribute__((__unused__)),
 		    event_asr_dispatch, eva);
 		tv.tv_sec = ar.ar_timeout / 1000;
 		tv.tv_usec = (ar.ar_timeout % 1000) * 1000;
-		event_add(&eva->ev, &tv);
+		if (event_add(&eva->ev, &tv)) {
+		    ar.ar_errno = errno;
+		    ar.ar_h_errno = NETDB_INTERNAL;
+		    eva->cb(&ar, eva->arg);
+		    free(eva);
+		}
 	}
 }
 

-- 
wbr, Kirill