linux-kernel - [PATCH 3.2 39/87] ipv6: tcp: add rcu locking in tcp_v6_send

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Date:	Mon, 08 Feb 2016 23:53:51 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Dave Jones" <davej@...emonkey.org.uk>
Subject: [PATCH 3.2 39/87] ipv6: tcp: add rcu locking in tcp_v6_send_synack()

3.2.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

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@...emonkey.org.uk>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv6/tcp_ipv6.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -513,8 +513,10 @@ static int tcp_v6_send_synack(struct soc
 		__tcp_v6_send_check(skb, &treq->loc_addr, &treq->rmt_addr);
 
 		ipv6_addr_copy(&fl6.daddr, &treq->rmt_addr);
+		rcu_read_lock();
 		err = ip6_xmit(sk, skb, &fl6, rcu_dereference(np->opt),
 			       np->tclass);
+		rcu_read_unlock();
 		err = net_xmit_eval(err);
 	}