ipv6: tcp: add rcu locking in tcp_v6_send_synack()

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>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6b8a8a9091fa..bd100b47c717 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -462,8 +462,10 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
                 if (np->repflow && ireq->pktopts)
                         fl6->flowlabel = ip6_flowlabel(ipv6_hdr(ireq->pktopts));
 
+                rcu_read_lock();
                 err = ip6_xmit(sk, skb, fl6, rcu_dereference(np->opt),
                                np->tclass);
+                rcu_read_unlock();
                 err = net_xmit_eval(err);
         }