Patch "tcp: do not mangle skb->cb[] in tcp_make_synack()" has been added to the 3.18-stable tree

Patch "tcp: do not mangle skb->cb[] in tcp_make_synack()" has been added to the 3.18-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    tcp: do not mangle skb->cb[] in tcp_make_synack()

to the 3.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-do-not-mangle-skb-cb-in-tcp_make_synack.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Tue Nov 21 15:37:44 CET 2017
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 2 Nov 2017 12:30:25 -0700
Subject: tcp: do not mangle skb->cb[] in tcp_make_synack()

From: Eric Dumazet <edumazet@google.com>


[ Upstream commit 3b11775033dc87c3d161996c54507b15ba26414a ]

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: 971f10eca186 ("tcp: better TCP_SKB_CB layout to reduce cache line misses")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Christoph Paasch <cpaasch@apple.com>
Reviewed-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_output.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2911,13 +2911,8 @@ struct sk_buff *tcp_make_synack(struct s
 	tcp_ecn_make_synack(req, th, sk);
 	th->source = htons(ireq->ir_num);
 	th->dest = ireq->ir_rmt_port;
-	/* 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);
 


Patches currently in stable-queue which might be from edumazet@google.com are

queue-3.18/tcp-do-not-mangle-skb-cb-in-tcp_make_synack.patch
queue-3.18/ipv6-dccp-do-not-inherit-ipv6_mc_list-from-parent.patch