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Commit 3b117750 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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tcp: do not mangle skb->cb[] in tcp_make_synack() 



Christoph Paasch sent a patch to address the following issue :

tcp_make_synack() is leaving some TCP private info in skb->cb[],
then send the packet by other means than tcp_transmit_skb()

tcp_transmit_skb() makes sure to clear skb->cb[] to not confuse
IPv4/IPV6 stacks, but we have no such cleanup for SYNACK.

tcp_make_synack() should not use tcp_init_nondata_skb() :

tcp_init_nondata_skb() really should be limited to skbs put in write/rtx
queues (the ones that are only sent via tcp_transmit_skb())

This patch fixes the issue and should even save few cpu cycles ;)

Fixes: 971f10ec ("tcp: better TCP_SKB_CB layout to reduce cache line misses")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarChristoph Paasch <cpaasch@apple.com>
Reviewed-by: default avatarChristoph Paasch <cpaasch@apple.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 25dd169a

net/ipv4/tcp_output.c

+2 −7
Original line number Diff line number Diff line
@@ -3180,13 +3180,8 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst, 
	th->source = htons(ireq->ir_num);

	th->dest = ireq->ir_rmt_port;

	skb->mark = ireq->ir_mark;

	/* Setting of flags are superfluous here for callers (and ECE is

	 * not even correctly set)

	 */

	tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,

			     TCPHDR_SYN | TCPHDR_ACK);



	th->seq = htonl(TCP_SKB_CB(skb)->seq);

	skb->ip_summed = CHECKSUM_PARTIAL;

	th->seq = htonl(tcp_rsk(req)->snt_isn);

	/* XXX data is queued and acked as is. No buffer/window check */

	th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);