Commit f2feaefd authored by Christoph Paasch's avatar Christoph Paasch Committed by David S. Miller
Browse files

tcp: Don't access TCP_SKB_CB before initializing it 



Since commit eeea10b8 ("tcp: add
tcp_v4_fill_cb()/tcp_v4_restore_cb()"), tcp_vX_fill_cb is only called
after tcp_filter(). That means, TCP_SKB_CB(skb)->end_seq still points to
the IP-part of the cb.

We thus should not mock with it, as this can trigger bugs (thanks
syzkaller):
[   12.349396] ==================================================================
[   12.350188] BUG: KASAN: slab-out-of-bounds in ip6_datagram_recv_specific_ctl+0x19b3/0x1a20
[   12.351035] Read of size 1 at addr ffff88006adbc208 by task test_ip6_datagr/1799

Setting end_seq is actually no more necessary in tcp_filter as it gets
initialized later on in tcp_vX_fill_cb.

Cc: Eric Dumazet <edumazet@google.com>
Fixes: eeea10b8 ("tcp: add tcp_v4_fill_cb()/tcp_v4_restore_cb()")
Signed-off-by: default avatarChristoph Paasch <cpaasch@apple.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0b31d98d

net/ipv4/tcp_ipv4.c

+1 −8
Original line number Diff line number Diff line
@@ -1734,15 +1734,8 @@ 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;

	return sk_filter_trim_cap(sk, skb, th->doff * 4);

}

EXPORT_SYMBOL(tcp_filter);