Commit ba34e6d9 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: make sure skb is not shared before using skb_get() 



IPv6 can keep a copy of SYN message using skb_get() in
tcp_v6_conn_request() so that caller wont free the skb when calling
kfree_skb() later.

Therefore TCP fast open has to clone the skb it is queuing in
child->sk_receive_queue, as all skbs consumed from receive_queue are
freed using __kfree_skb() (ie assuming skb->users == 1)

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Fixes: 5b7ed089 ("tcp: move fastopen functions to tcp_fastopen.c")
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 96727239

net/ipv4/tcp_fastopen.c

+24 −8
Original line number Diff line number Diff line
@@ -134,6 +134,7 @@ static bool tcp_fastopen_create_child(struct sock *sk, 
	struct tcp_sock *tp;

	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;

	struct sock *child;

	u32 end_seq;



	req->num_retrans = 0;

	req->num_timeout = 0;
@@ -185,20 +186,35 @@ static bool tcp_fastopen_create_child(struct sock *sk, 


	/* Queue the data carried in the SYN packet. We need to first

	 * bump skb's refcnt because the caller will attempt to free it.

	 * Note that IPv6 might also have used skb_get() trick

	 * in tcp_v6_conn_request() to keep this SYN around (treq->pktopts)

	 * So we need to eventually get a clone of the packet,

	 * before inserting it in sk_receive_queue.

	 *

	 * XXX (TFO) - we honor a zero-payload TFO request for now,

	 * (any reason not to?) but no need to queue the skb since

	 * there is no data. How about SYN+FIN?

	 */

	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1) {

		skb = skb_get(skb);

		skb_dst_drop(skb);

		__skb_pull(skb, tcp_hdr(skb)->doff * 4);

		skb_set_owner_r(skb, child);

		__skb_queue_tail(&child->sk_receive_queue, skb);

	end_seq = TCP_SKB_CB(skb)->end_seq;

	if (end_seq != TCP_SKB_CB(skb)->seq + 1) {

		struct sk_buff *skb2;



		if (unlikely(skb_shared(skb)))

			skb2 = skb_clone(skb, GFP_ATOMIC);

		else

			skb2 = skb_get(skb);



		if (likely(skb2)) {

			skb_dst_drop(skb2);

			__skb_pull(skb2, tcp_hdrlen(skb));

			skb_set_owner_r(skb2, child);

			__skb_queue_tail(&child->sk_receive_queue, skb2);

			tp->syn_data_acked = 1;

		} else {

			end_seq = TCP_SKB_CB(skb)->seq + 1;

		}

	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;

	}

	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = end_seq;

	sk->sk_data_ready(sk);

	bh_unlock_sock(child);

	sock_put(child);

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