Commit b738a185 authored Mar 19, 2020 by Eric Dumazet Committed by David S. Miller Mar 19, 2020

tcp: ensure skb->dev is NULL before leaving TCP stack



skb->rbnode is sharing three skb fields : next, prev, dev

When a packet is sent, TCP keeps the original skb (master)
in a rtx queue, which was converted to rbtree a while back.

__tcp_transmit_skb() is responsible to clone the master skb,
and add the TCP header to the clone before sending it
to network layer.

skb_clone() already clears skb->next and skb->prev, but copies
the master oskb->dev into the clone.

We need to clear skb->dev, otherwise lower layers could interpret
the value as a pointer to a netdev.

This old bug surfaced recently when commit 28f8bfd1
("netfilter: Support iif matches in POSTROUTING") was merged.

Before this netfilter commit, skb->dev value was ignored and
changed before reaching dev_queue_xmit()

Fixes: 75c119af ("tcp: implement rb-tree based retransmit queue")
Fixes: 28f8bfd1 ("netfilter: Support iif matches in POSTROUTING")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Martin Zaharinov <micron10@gmail.com>
Cc: Florian Westphal <fw@strlen.de>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent f1f20a86

net/ipv4/tcp_output.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -1109,6 +1109,10 @@ static int __tcp_transmit_skb(struct sock sk, struct sk_buff skb,

		if (unlikely(!skb))
		return -ENOBUFS;
		/* retransmit skbs might have a non zero value in skb->dev
		* because skb->dev is aliased with skb->rbnode.rb_left
		*/
		skb->dev = NULL;
		}

		inet = inet_sk(sk);

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