[3.16.y-ckt stable] Patch "ipv6: tcp: add rcu locking in tcp_v6_send_synack()" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ipv6: tcp: add rcu locking in tcp_v6_send_synack()

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt24.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

---8<------------------------------------------------------------

>From 2e0009900a7280500df2fe4a988caa5c24305d2a Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet at google.com>
Date: Fri, 8 Jan 2016 09:35:51 -0800
Subject: ipv6: tcp: add rcu locking in tcp_v6_send_synack()

commit 3e4006f0b86a5ae5eb0e8215f9a9e1db24506977 upstream.

When first SYNACK is sent, we already hold rcu_read_lock(), but this
is not true if a SYNACK is retransmitted, as a timer (soft) interrupt
does not hold rcu_read_lock()

Fixes: 45f6fad84cc30 ("ipv6: add complete rcu protection around np->opt")
Reported-by: Dave Jones <davej at codemonkey.org.uk>
Signed-off-by: Eric Dumazet <edumazet at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ipv6/tcp_ipv6.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 9a87a208732e..2350f12eb318 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -497,8 +497,10 @@ static int tcp_v6_send_synack(struct sock *sk, struct dst_entry *dst,
 			fl6->flowlabel = ip6_flowlabel(ipv6_hdr(ireq->pktopts));

 		skb_set_queue_mapping(skb, queue_mapping);
+		rcu_read_lock();
 		err = ip6_xmit(sk, skb, fl6, rcu_dereference(np->opt),
 			       np->tclass);
+		rcu_read_unlock();
 		err = net_xmit_eval(err);
 	}