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Commit ac6e7800 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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tcp: take care of truncations done by sk_filter() 



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: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarMarco Grassi <marco.gra@gmail.com>
Reported-by: default avatarVladis Dronov <vdronov@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 969447f2

include/net/tcp.h

+1 −0
Original line number Diff line number Diff line
@@ -1220,6 +1220,7 @@ static inline void tcp_prequeue_init(struct tcp_sock *tp) 


bool tcp_prequeue(struct sock *sk, struct sk_buff *skb);

bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb);

int tcp_filter(struct sock *sk, struct sk_buff *skb);



#undef STATE_TRACE

net/ipv4/tcp_ipv4.c

+18 −1
Original line number Diff line number Diff line
@@ -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 @@ int tcp_v4_rcv(struct sk_buff *skb) 


	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;

net/ipv6/tcp_ipv6.c

+4 −2
Original line number Diff line number Diff line
@@ -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 (tcp_filter(sk, skb))

		goto discard;



	/*
@@ -1457,8 +1457,10 @@ 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 (tcp_filter(sk, skb))

		goto discard_and_relse;

	th = (const struct tcphdr *)skb->data;

	hdr = ipv6_hdr(skb);



	skb->dev = NULL;