From f291f1ee9434f56d4b185db0652794a92e313b00 Mon Sep 17 00:00:00 2001 From: Donatas Abraitis Date: Tue, 22 Aug 2023 22:52:04 +0300 Subject: [PATCH] bgpd: Do not process NLRIs if the attribute length is zero ``` 3 0x00007f423aa42476 in __GI_raise (sig=sig@entry=11) at ../sysdeps/posix/raise.c:26 4 0x00007f423aef9740 in core_handler (signo=11, siginfo=0x7fffc414deb0, context=) at lib/sigevent.c:246 5 6 0x0000564dea2fc71e in route_set_aspath_prepend (rule=0x564debd66d50, prefix=0x7fffc414ea30, object=0x7fffc414e400) at bgpd/bgp_routemap.c:2258 7 0x00007f423aeec7e0 in route_map_apply_ext (map=, prefix=prefix@entry=0x7fffc414ea30, match_object=match_object@entry=0x7fffc414e400, set_object=set_object@entry=0x7fffc414e400, pref=pref@entry=0x0) at lib/routemap.c:2690 8 0x0000564dea2d277e in bgp_input_modifier (peer=peer@entry=0x7f4238f59010, p=p@entry=0x7fffc414ea30, attr=attr@entry=0x7fffc414e770, afi=afi@entry=AFI_IP, safi=safi@entry=SAFI_UNICAST, rmap_name=rmap_name@entry=0x0, label=0x0, num_labels=0, dest=0x564debdd5130) at bgpd/bgp_route.c:1772 9 0x0000564dea2df762 in bgp_update (peer=peer@entry=0x7f4238f59010, p=p@entry=0x7fffc414ea30, addpath_id=addpath_id@entry=0, attr=0x7fffc414eb50, afi=afi@entry=AFI_IP, safi=, safi@entry=SAFI_UNICAST, type=9, sub_type=0, prd=0x0, label=0x0, num_labels=0, soft_reconfig=0, evpn=0x0) at bgpd/bgp_route.c:4374 10 0x0000564dea2e2047 in bgp_nlri_parse_ip (peer=0x7f4238f59010, attr=attr@entry=0x7fffc414eb50, packet=0x7fffc414eaf0) at bgpd/bgp_route.c:6249 11 0x0000564dea2c5a58 in bgp_nlri_parse (peer=peer@entry=0x7f4238f59010, attr=attr@entry=0x7fffc414eb50, packet=packet@entry=0x7fffc414eaf0, mp_withdraw=mp_withdraw@entry=false) at bgpd/bgp_packet.c:339 12 0x0000564dea2c5d66 in bgp_update_receive (peer=peer@entry=0x7f4238f59010, size=size@entry=109) at bgpd/bgp_packet.c:2024 13 0x0000564dea2c901d in bgp_process_packet (thread=) at bgpd/bgp_packet.c:2933 14 0x00007f423af0bf71 in event_call (thread=thread@entry=0x7fffc414ee40) at lib/event.c:1995 15 0x00007f423aebb198 in frr_run (master=0x564deb73c670) at lib/libfrr.c:1213 16 0x0000564dea261b83 in main (argc=, argv=) at bgpd/bgp_main.c:505 ``` With the configuration: ``` frr version 9.1-dev-MyOwnFRRVersion frr defaults traditional hostname ip-172-31-13-140 log file /tmp/debug.log log syslog service integrated-vtysh-config ! debug bgp keepalives debug bgp neighbor-events debug bgp updates in debug bgp updates out ! router bgp 100 bgp router-id 9.9.9.9 no bgp ebgp-requires-policy bgp bestpath aigp neighbor 172.31.2.47 remote-as 200 ! address-family ipv4 unicast neighbor 172.31.2.47 default-originate neighbor 172.31.2.47 route-map RM_IN in exit-address-family exit ! route-map RM_IN permit 10 set as-path prepend 200 exit ! ``` The issue is that we try to process NLRIs even if the attribute length is 0. Later bgp_update() will handle route-maps and a crash occurs because all the attributes are NULL, including aspath, where we dereference. According to the RFC 4271: A value of 0 indicates that neither the Network Layer Reachability Information field nor the Path Attribute field is present in this UPDATE message. But with a fuzzed UPDATE message this can be faked. I think it's reasonable to skip processing NLRIs if both update_len and attribute_len are 0. Reported-by: Iggy Frankovic Signed-off-by: Donatas Abraitis (cherry picked from commit 28ccc24d38df1d51ed8a563507e5d6f6171fdd38) --- bgpd/bgp_packet.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/bgpd/bgp_packet.c b/bgpd/bgp_packet.c index 60f1dcbcd..a02d54894 100644 --- a/bgpd/bgp_packet.c +++ b/bgpd/bgp_packet.c @@ -1983,7 +1983,7 @@ 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) { + if (update_len && attribute_len) { /* Set NLRI portion to structure. */ nlris[NLRI_UPDATE].afi = AFI_IP; nlris[NLRI_UPDATE].safi = SAFI_UNICAST; -- 2.39.2