imap-send: handle missing response codes gracefully

rscharfe · gitster · commit 618ec81abbda · 2017-11-03T22:45:57.000+09:00
Response codes are optional.  Exit parse_response_code() early if it's
passed a NULL string, indicating that we reached the end of the reply.
This avoids dereferencing said NULL pointer.

Noticed-by: Junio C Hamano &lt;gitster@pobox.com&gt;
Signed-off-by: Rene Scharfe &lt;l.s.r@web.de&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/imap-send.c b/imap-send.c
@@ -683,7 +683,7 @@ static int parse_response_code(struct imap_store *ctx, struct imap_cmd_cb *cb,
 	struct imap *imap = ctx->imap;
 	char *arg, *p;
 
-	if (*s != '[')
+	if (!s || *s != '[')
 		return RESP_OK;		/* no response code */
 	s++;
 	if (!(p = strchr(s, ']'))) {
