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tcp: take care of truncations done by sk_filter()

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With syzkaller help, Marco Grassi found a bug in TCP stack,
crashing in tcp_collapse()

Root cause is that sk_filter() can truncate the incoming skb,
but TCP stack was not really expecting this to happen.
It probably was expecting a simple DROP or ACCEPT behavior.

We first need to make sure no part of TCP header could be removed.
Then we need to adjust TCP_SKB_CB(skb)->end_seq

Many thanks to syzkaller team and Marco for giving us a reproducer.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Marco Grassi <marco.gra@gmail.com>
Reported-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2016-11-10 13:12:35 -08:00
committed by David S. Miller
parent 969447f226
commit ac6e780070
3 changed files with 23 additions and 3 deletions
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19
net/ipv4/tcp_ipv4.c
View File

@@ -1564,6 +1564,21 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)
}
EXPORT_SYMBOL(tcp_add_backlog);
int tcp_filter(struct sock *sk, struct sk_buff *skb)
{
struct tcphdr *th = (struct tcphdr *)skb->data;
unsigned int eaten = skb->len;
int err;
err = sk_filter_trim_cap(sk, skb, th->doff * 4);
if (!err) {
eaten -= skb->len;
TCP_SKB_CB(skb)->end_seq -= eaten;
}
return err;
}
EXPORT_SYMBOL(tcp_filter);
/*
* From tcp_input.c
*/
@@ -1676,8 +1691,10 @@ process:
nf_reset(skb);
if (sk_filter(sk, skb))
if (tcp_filter(sk, skb))
goto discard_and_relse;
th = (const struct tcphdr *)skb->data;
iph = ip_hdr(skb);
skb->dev = NULL;