[PATCH] ping: implement proper locking

[Paolo Pisati]

From: Eric Dumazet <edumazet at google.com>

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 at google.com>
Reported-by: Daniel Jiang <danieljiang0415 at gmail.com>
Reported-by: Solar Designer <solar at openwall.com>
Reported-by: Andrey Konovalov <andreyknvl at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 43a6684519ab0a6c52024b5e25322476cabad893)
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 net/ipv4/ping.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 9161342..71a35e1 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -150,17 +150,18 @@ void ping_hash(struct sock *sk)
 void ping_unhash(struct sock *sk)
 {
 	struct inet_sock *isk = inet_sk(sk);
+
 	pr_debug("ping_unhash(isk=%p,isk->num=%u)\n", isk, isk->inet_num);
+	write_lock_bh(&ping_table.lock);
 	if (sk_hashed(sk)) {
-		write_lock_bh(&ping_table.lock);
 		hlist_nulls_del(&sk->sk_nulls_node);
 		sk_nulls_node_init(&sk->sk_nulls_node);
 		sock_put(sk);
 		isk->inet_num = 0;
 		isk->inet_sport = 0;
 		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
-		write_unlock_bh(&ping_table.lock);
 	}
+	write_unlock_bh(&ping_table.lock);
 }
 EXPORT_SYMBOL_GPL(ping_unhash);
 
-- 
2.7.4