commit 98b6dee90d3fd7300cc834972decd2c123af999c
from: Omar Polo <op@omarpolo.com>
date: Fri Jan 28 12:38:01 2022 UTC

only memcpy into imsg->data if datalen is not zero

Passing a NULL pointer to memcpy is UB no matter if len is 0 (commit by
claudio@, backporting for telescope.)

commit - 6d5348f32514004ad33d27ece8dec68ffed9b209
commit + 98b6dee90d3fd7300cc834972decd2c123af999c
blob - 6c746751450bd523a4fb6736a4347900fd01d5bb
blob + 59998a5321d7c7e0dc8c44be2e5371e1213a7371
--- compat/imsg.c
+++ compat/imsg.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: imsg.c,v 1.16 2017/12/14 09:27:44 kettenis Exp $	*/
+/*	$OpenBSD: imsg.c,v 1.17 2022/01/28 10:41:44 claudio Exp $	*/
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -151,7 +151,8 @@ imsg_get(struct imsgbuf *ibuf, struct imsg *imsg)
 	else
 		imsg->fd = -1;
 
-	memcpy(imsg->data, ibuf->r.rptr, datalen);
+	if (datalen != 0)
+		memcpy(imsg->data, ibuf->r.rptr, datalen);
 
 	if (imsg->hdr.len < av) {
 		left = av - imsg->hdr.len;