Re: BUG() can be hit in tcp_collapse()

[Eric Dumazet]

On Thu, 2016-11-10 at 11:49 -0800, Eric Dumazet wrote:
> 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 :

Another sk_filter() is used in tcp v6.
So the correct patch would be :

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..96525649a397 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;
 
        /*
@@ -1457,7 +1457,7 @@ static int tcp_v6_rcv(struct sk_buff *skb)
        if (tcp_v6_inbound_md5_hash(sk, skb))
                goto discard_and_relse;
 
-       if (sk_filter(sk, skb))
+       if (sk_filter_trim_cap(sk, skb, skb->len))
                goto discard_and_relse;
 
        skb->dev = NULL;