netdev - [PATCH net] ipv6: tcp: add rcu locking in tcp_v6_send

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Message-ID: <1452274551.8255.232.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 08 Jan 2016 09:35:51 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Jones <davej@...emonkey.org.uk>,
	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: [PATCH net] ipv6: tcp: add rcu locking in tcp_v6_send_synack()

From: Eric Dumazet <edumazet@...gle.com>

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@...emonkey.org.uk>
Signed-off-by: Eric Dumazet <edumazet@...gle.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 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);
 	}