From 7b4fdf77a450ec0fdcb2f677b080ddbf2c186544 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Fri, 3 Mar 2017 21:44:00 +0100 Subject: [PATCH] netfilter: don't track fragmented packets Andrey reports syzkaller splat caused by NF_CT_ASSERT(!ip_is_fragment(ip_hdr(skb))); in ipv4 nat. But this assertion (and the comment) are wrong, this function does see fragments when IP_NODEFRAG setsockopt is used. As conntrack doesn't track packets without complete l4 header, only the first fragment is tracked. Because applying nat to first packet but not the rest makes no sense this also turns off tracking of all fragments. Reported-by: Andrey Konovalov Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c | 4 ++++ net/ipv4/netfilter/nf_nat_l3proto_ipv4.c | 5 ----- 2 files changed, 4 insertions(+), 5 deletions(-) diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c index bc1486f2c06433..2e14ed11a35cfc 100644 --- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c +++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c @@ -165,6 +165,10 @@ static unsigned int ipv4_conntrack_local(void *priv, if (skb->len < sizeof(struct iphdr) || ip_hdrlen(skb) < sizeof(struct iphdr)) return NF_ACCEPT; + + if (ip_is_fragment(ip_hdr(skb))) /* IP_NODEFRAG setsockopt set */ + return NF_ACCEPT; + return nf_conntrack_in(state->net, PF_INET, state->hook, skb); } diff --git a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c b/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c index f8aad03d674b05..6f5e8d01b87693 100644 --- a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c +++ b/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c @@ -255,11 +255,6 @@ nf_nat_ipv4_fn(void *priv, struct sk_buff *skb, /* maniptype == SRC for postrouting. */ enum nf_nat_manip_type maniptype = HOOK2MANIP(state->hook); - /* We never see fragments: conntrack defrags on pre-routing - * and local-out, and nf_nat_out protects post-routing. - */ - NF_CT_ASSERT(!ip_is_fragment(ip_hdr(skb))); - ct = nf_ct_get(skb, &ctinfo); /* Can't track? It's not due to stress, or conntrack would * have dropped it. Hence it's the user's responsibilty to