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 4.13-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

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-4.13 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 13:07:20 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 @@ -3207,13 +3207,8 @@ struct sk_buff *tcp_make_synack(const st 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);

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

queue-4.13/tcp-fix-tcp_fastretrans_alert-warning.patch queue-4.13/tcp-do-not-mangle-skb-cb-in-tcp_make_synack.patch queue-4.13/tcp-gso-avoid-refcount_t-warning-from-tcp_gso_segment.patch