From: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
Date: Sun, 12 Apr 2020 16:53:05 +0000 (+0100)
Subject: dns.c: improve input validation
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=e74a3f9883199e9db7220d52b78e5fbdb4441ca3;p=oweals%2Fmdnsd.git

dns.c: improve input validation

dns.c scan_name() add more input validation
parse_answer() add remaining length check
dns_handle_packet() add remaining length check

Addresses CVE-2020-11750

Thanks to Guido Vranken <guido@guidovranken.com> for the report who
requested credit be given to 'ForAllSecure Mayhem'.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
---

diff --git a/dns.c b/dns.c
index 86e5ea3..c64f3b1 100644
--- a/dns.c
+++ b/dns.c
@@ -222,6 +222,7 @@ scan_name(const uint8_t *buffer, int len)
 		if (IS_COMPRESSED(l))
 			return offset + 2;
 
+		if (l + 1 > len) return -1;
 		len -= l + 1;
 		offset += l + 1;
 		buffer += l + 1;
@@ -317,7 +318,7 @@ static int parse_answer(struct interface *iface, struct sockaddr *from,
 	struct dns_answer *a;
 	uint8_t *rdata;
 
-	if (!name) {
+	if (!name || rlen < 0) {
 		fprintf(stderr, "dropping: bad question\n");
 		return -1;
 	}
@@ -421,7 +422,7 @@ dns_handle_packet(struct interface *iface, struct sockaddr *from, uint16_t port,
 		char *name = dns_consume_name(buffer, len, &b, &rlen);
 		struct dns_question *q;
 
-		if (!name) {
+		if (!name || rlen < 0) {
 			fprintf(stderr, "dropping: bad name\n");
 			return;
 		}