Patch "tcp: do not mangle skb->cb[] in tcp_make_synack()" has been added to the 4.13-stable tree

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;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-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Thu, 2 Nov 2017 12:30:25 -0700
Subject: tcp: do not mangle skb->cb[] in tcp_make_synack()

From: Eric Dumazet <[email protected]>

[ 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 ;)

---
 net/ipv4/tcp_output.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

@@ -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 [email protected] 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