netdev - Re: BUG() can be hit in tcp

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Date:   Thu, 10 Nov 2016 11:49:26 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vladis Dronov <vdronov@...hat.com>
Cc:     netdev@...r.kernel.org, stable@...r.kernel.org,
        Marco Grassi <marco.gra@...il.com>
Subject: Re: BUG() can be hit in tcp_collapse()

On Thu, 2016-11-10 at 11:26 -0800, Eric Dumazet wrote:

> The issue is that sk_filter() truncates an incoming packet to a smaller
> value.
> 
> Bad things happen because TCP_SKB_CB(skb)->end_seq is not updated.
> 
> I guess other issues would also happen if the truncation also removes
> part of tcp header.
> 
> sk_filter_trim_cap(sk, skb, tcp_hlen) would be needed,
> or sk_filter_trim_cap(sk, skb, skb->len) to only ACCEPT/DROP packets,
> but no truncations.

Something like :

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 61b7be303eec..0b8f575eefaa 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1676,7 +1676,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 
 	nf_reset(skb);
 
-	if (sk_filter(sk, skb))
+	if (sk_filter_trim_cap(sk, skb, skb->len))
 		goto discard_and_relse;
 
 	skb->dev = NULL;
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6ca23c2e76f7..2c7a6f7f1113 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1229,7 +1229,7 @@ static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 	if (skb->protocol == htons(ETH_P_IP))
 		return tcp_v4_do_rcv(sk, skb);
 
-	if (sk_filter(sk, skb))
+	if (sk_filter_trim_cap(sk, skb, skb->len))
 		goto discard;
 
 	/*