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@codemonkey.org.uk>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 9a87a208732e823c64a2e9f9e50d9c639a0b65e0..2350f12eb318154b0cfc0e0297c0e6e550933208 100644 (file)
--- 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);
        }