From 4e39893cfb2d4dbc13fa6d6a25bbf623ed14a4fb Mon Sep 17 00:00:00 2001
From: Donatas Abraitis <donatas@opensourcerouting.org>
Date: Sun, 29 Oct 2023 22:44:45 +0200
Subject: [PATCH] bgpd: Ignore handling NLRIs if we received MP_UNREACH_NLRI
Upstream: yes
CVE-2023-47234,bsc#1216897,https://github.com/FRRouting/frr/pull/14716/commits/c37119df45bbf4ef713bc10475af2ee06e12f3bf

If we receive MP_UNREACH_NLRI, we should stop handling remaining NLRIs if
no mandatory path attributes received.

In other words, if MP_UNREACH_NLRI received, the remaining NLRIs should be handled
as a new data, but without mandatory attributes, it's a malformed packet.

In normal case, this MUST not happen at all, but to avoid crashing bgpd, we MUST
handle that.

Reported-by: Iggy Frankovic <iggyfran@amazon.com>
Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>
Signed-off-by: Marius Tomaschewski <mt@suse.com>

diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c
index fc92dbb326..ae0f052c42 100644
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -3112,15 +3112,6 @@ static int bgp_attr_check(struct peer *peer, struct attr *attr,
 	    !length)
 		return BGP_ATTR_PARSE_WITHDRAW;
 
-	/* "An UPDATE message that contains the MP_UNREACH_NLRI is not required
-	   to carry any other path attributes.", though if MP_REACH_NLRI or NLRI
-	   are present, it should.  Check for any other attribute being present
-	   instead.
-	 */
-	if ((!CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_MP_REACH_NLRI)) &&
-	     CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_MP_UNREACH_NLRI))))
-		return BGP_ATTR_PARSE_PROCEED;
-
 	if (!CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_ORIGIN)))
 		type = BGP_ATTR_ORIGIN;
 
@@ -3139,6 +3130,16 @@ static int bgp_attr_check(struct peer *peer, struct attr *attr,
 	    && !CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_LOCAL_PREF)))
 		type = BGP_ATTR_LOCAL_PREF;
 
+	/* An UPDATE message that contains the MP_UNREACH_NLRI is not required
+	 * to carry any other path attributes. Though if MP_REACH_NLRI or NLRI
+	 * are present, it should. Check for any other attribute being present
+	 * instead.
+	 */
+	if (!CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_MP_REACH_NLRI)) &&
+	    CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_MP_UNREACH_NLRI)))
+		return type ? BGP_ATTR_PARSE_MISSING_MANDATORY
+			    : BGP_ATTR_PARSE_PROCEED;
+
 	/* If any of the well-known mandatory attributes are not present
 	 * in an UPDATE message, then "treat-as-withdraw" MUST be used.
 	 */
diff --git a/bgpd/bgp_attr.h b/bgpd/bgp_attr.h
index 23767153b2..27708c0689 100644
--- a/bgpd/bgp_attr.h
+++ b/bgpd/bgp_attr.h
@@ -382,6 +382,7 @@ enum bgp_attr_parse_ret {
 	/* only used internally, send notify + convert to BGP_ATTR_PARSE_ERROR
 	 */
 	BGP_ATTR_PARSE_ERROR_NOTIFYPLS = -3,
+	BGP_ATTR_PARSE_MISSING_MANDATORY = -4,
 };
 
 struct bpacket_attr_vec_arr;
diff --git a/bgpd/bgp_packet.c b/bgpd/bgp_packet.c
index 20c642190b..b175a26ab9 100644
--- a/bgpd/bgp_packet.c
+++ b/bgpd/bgp_packet.c
@@ -1951,7 +1951,12 @@ static int bgp_update_receive(struct peer *peer, bgp_size_t size)
 	/* Network Layer Reachability Information. */
 	update_len = end - stream_pnt(s);
 
-	if (update_len && attribute_len) {
+	/* If we received MP_UNREACH_NLRI attribute, but also NLRIs, then
+	 * NLRIs should be handled as a new data. Though, if we received
+	 * NLRIs without mandatory attributes, they should be ignored.
+	 */
+	if (update_len && attribute_len &&
+	    attr_parse_ret != BGP_ATTR_PARSE_MISSING_MANDATORY) {
 		/* Set NLRI portion to structure. */
 		nlris[NLRI_UPDATE].afi = AFI_IP;
 		nlris[NLRI_UPDATE].safi = SAFI_UNICAST;
-- 
2.35.3