ping: implement proper locking

ping: implement proper locking

We got a report of yet another bug in ping

http://www.openwall.com/lists/oss-security/2017/03/24/6

->disconnect() is not called with socket lock held.

Fix this by acquiring ping rwlock earlier.

Thanks to Daniel, Alexander and Andrey for letting us know this problem.

Fixes: c319b4d76b9e ("net: ipv4: add IPPROTO_ICMP socket kind")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Daniel Jiang <danieljiang0415@gmail.com>
Reported-by: Solar Designer <solar@openwall.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 43a6684519ab0a6c52024b5e25322476cabad893)

Orabug: 25883225
CEV: CVE-2017-2671

Signed-off-by: Tim Tianyang Chen <tianyang.chen@oracle.com>
Reviewed-by: Dhaval Giani <dhaval.giani@oracle.com>