sctp: unbalanced rcu lock in ip_queue_xmit()

The bug was introduced in 2.6.32.61 by commit b8710128e201 ("inet: add RCU
protection to inet->opt") (it's a backport of upstream commit f6d8bd051c39).

In SCTP case, packet is already routed, hence we jump to the label
'packet_routed', but without rcu_read_lock(). After this label,
rcu_read_unlock() is called unconditionally.

Spotted-by: Guo Fengtian <fengtian.guo@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 7dde039374e4c0658853ede9aa4f83346fbd91f8..2cd69e3497ad6c4e58191b3ef8928c9447ca22aa 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -320,13 +320,13 @@ int ip_queue_xmit(struct sk_buff *skb, int ipfragok)
        /* Skip all of this if the packet is already routed,
         * f.e. by something like SCTP.
         */
+       rcu_read_lock();
        rt = skb_rtable(skb);
        if (rt != NULL)
                goto packet_routed;
 
        /* Make sure we can route this packet. */
        rt = (struct rtable *)__sk_dst_check(sk, 0);
-       rcu_read_lock();
        inet_opt = rcu_dereference(inet->inet_opt);
        if (rt == NULL) {
                __be32 daddr;