From 2b272bb558f1d3a5aa95ed8a82253786fd1a48ba Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Mon, 30 Jan 2023 11:39:29 +0100 Subject: [PATCH 1/2] netfilter: br_netfilter: disable sabotage_in hook after first suppression When using a xfrm interface in a bridged setup (the outgoing device is bridged), the incoming packets in the xfrm interface are only tracked in the outgoing direction. $ brctl show bridge name interfaces br_eth1 eth1 $ conntrack -L tcp 115 SYN_SENT src=192... dst=192... [UNREPLIED] ... If br_netfilter is enabled, the first (encrypted) packet is received onR eth1, conntrack hooks are called from br_netfilter emulation which allocates nf_bridge info for this skb. If the packet is for local machine, skb gets passed up the ip stack. The skb passes through ip prerouting a second time. br_netfilter ip_sabotage_in supresses the re-invocation of the hooks. After this, skb gets decrypted in xfrm layer and appears in network stack a second time (after decryption). Then, ip_sabotage_in is called again and suppresses netfilter hook invocation, even though the bridge layer never called them for the plaintext incarnation of the packet. Free the bridge info after the first suppression to avoid this. I was unable to figure out where the regression comes from, as far as i can see br_netfilter always had this problem; i did not expect that skb is looped again with different headers. Fixes: c4b0e771f906 ("netfilter: avoid using skb->nf_bridge directly") Reported-and-tested-by: Wolfgang Nothdurft Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/bridge/br_netfilter_hooks.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c index f20f4373ff40..9554abcfd5b4 100644 --- a/net/bridge/br_netfilter_hooks.c +++ b/net/bridge/br_netfilter_hooks.c @@ -871,6 +871,7 @@ static unsigned int ip_sabotage_in(void *priv, if (nf_bridge && !nf_bridge->in_prerouting && !netif_is_l3_master(skb->dev) && !netif_is_l3_slave(skb->dev)) { + nf_bridge_info_free(skb); state->okfn(state->net, state->sk, skb); return NF_STOLEN; } From bd0e06f0def75ba26572a94e5350324474a55562 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Thu, 26 Jan 2023 02:35:21 +0100 Subject: [PATCH 2/2] Revert "netfilter: conntrack: fix bug in for_each_sctp_chunk" There is no bug. If sch->length == 0, this would result in an infinite loop, but first caller, do_basic_checks(), errors out in this case. After this change, packets with bogus zero-length chunks are no longer detected as invalid, so revert & add comment wrt. 0 length check. Fixes: 98ee00774525 ("netfilter: conntrack: fix bug in for_each_sctp_chunk") Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_proto_sctp.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/netfilter/nf_conntrack_proto_sctp.c b/net/netfilter/nf_conntrack_proto_sctp.c index 945dd40e7077..011d414038ea 100644 --- a/net/netfilter/nf_conntrack_proto_sctp.c +++ b/net/netfilter/nf_conntrack_proto_sctp.c @@ -142,10 +142,11 @@ static void sctp_print_conntrack(struct seq_file *s, struct nf_conn *ct) } #endif +/* do_basic_checks ensures sch->length > 0, do not use before */ #define for_each_sctp_chunk(skb, sch, _sch, offset, dataoff, count) \ for ((offset) = (dataoff) + sizeof(struct sctphdr), (count) = 0; \ - ((sch) = skb_header_pointer((skb), (offset), sizeof(_sch), &(_sch))) && \ - (sch)->length; \ + (offset) < (skb)->len && \ + ((sch) = skb_header_pointer((skb), (offset), sizeof(_sch), &(_sch))); \ (offset) += (ntohs((sch)->length) + 3) & ~3, (count)++) /* Some validity checks to make sure the chunks are fine */