From 837f57f087c997e3d66f7d1f86bdec3149917aba Mon Sep 17 00:00:00 2001 From: Donatas Abraitis Date: Fri, 27 Oct 2023 11:56:45 +0300 Subject: [PATCH 1/2] bgpd: Treat EOR as withdrawn to avoid unwanted handling of malformed attrs Treat-as-withdraw, otherwise if we just ignore it, we will pass it to be processed as a normal UPDATE without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 (cherry picked from commit 6814f2e0138a6ea5e1f83bdd9085d9a77999900b) --- 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 bf33e8e3ec..638546ed21 100644 --- a/bgpd/bgp_attr.c +++ b/bgpd/bgp_attr.c @@ -3391,10 +3391,13 @@ 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 && !length) - return BGP_ATTR_PARSE_PROCEED; + 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 @@ -3889,7 +3892,13 @@ done: aspath_unintern(&as4_path); transit = bgp_attr_get_transit(attr); - 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 (transit) bgp_attr_set_transit(attr, transit_intern(transit)); From 250844bbcabcc55d9cc009c0769718a4f2a1e166 Mon Sep 17 00:00:00 2001 From: Donatas Abraitis Date: Sun, 29 Oct 2023 22:44:45 +0200 Subject: [PATCH 2/2] bgpd: Ignore handling NLRIs if we received MP_UNREACH_NLRI 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 Signed-off-by: Donatas Abraitis (cherry picked from commit c37119df45bbf4ef713bc10475af2ee06e12f3bf) --- bgpd/bgp_attr.c | 19 ++++++++++--------- bgpd/bgp_attr.h | 1 + bgpd/bgp_packet.c | 7 ++++++- 3 files changed, 17 insertions(+), 10 deletions(-) diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c index 638546ed21..56e77eb3a7 100644 --- a/bgpd/bgp_attr.c +++ b/bgpd/bgp_attr.c @@ -3399,15 +3399,6 @@ 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; @@ -3426,6 +3417,16 @@ 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 fc347e7a1b..d30155e6db 100644 --- a/bgpd/bgp_attr.h +++ b/bgpd/bgp_attr.h @@ -364,6 +364,7 @@ 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 8fbdce56a2..cae82cbbb7 100644 --- a/bgpd/bgp_packet.c +++ b/bgpd/bgp_packet.c @@ -2165,7 +2165,12 @@ static int bgp_update_receive(struct peer_connection *connection, /* 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;