commit 5c6a65504e44766a5cf8d0b9131bd2c2331ee8ca
from: Martijn van Duren <martijn@openbsd.org>
date: Thu Mar 24 18:59:51 2022 UTC

Make sure we don't crash on invalid headers

commit - 1c524edbef28493e3150e965d4d17cf05f705277
commit + 5c6a65504e44766a5cf8d0b9131bd2c2331ee8ca
blob - 12c43a2f8a238a8ed27a39b174092cf014e5c243
blob + b20aa0b202fd630f75db94bf7facc5cbdcea8b07
--- main.c
+++ main.c
@@ -325,8 +325,10 @@ dkim_header_add(struct osmtpd_ctx *ctx, const char *li
 			start = msg->header[msg->nheaders - 1].buf;
 			end = osmtpd_mheader_skip_fieldname(start, 0);
 			/* In case someone uses an obs-optional */
-			verify = osmtpd_mheader_skip_wsp(end, 1);
-			if (strncasecmp(
+			if (end != NULL)
+				verify = osmtpd_mheader_skip_wsp(end, 1);
+			if (end != NULL &&
+			    strncasecmp(
 			    start, "DKIM-Signature", end - start) == 0 &&
 			    verify[0] == ':')
 				dkim_signature_parse(