net/ping: handle protocol mismatching scenario

ping_lookup() may return a wrong sock if sk_buff's and sock's protocols
dont' match. For example, sk_buff's protocol is ETH_P_IPV6, but sock's
sk_family is AF_INET, in that case, if sk->sk_bound_dev_if is zero, a wrong
sock will be returned.
the fix is to "continue" the searching, if no matching, return NULL.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Cc: netdev@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: NJane Zhou <a17711@motorola.com>
Signed-off-by: NYiwei Zhao <gbjc64@motorola.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ping.c

@@ -217,6 +217,8 @@ static struct sock *ping_lookup(struct net *net, struct sk_buff *skb, u16 ident)
 					     &ipv6_hdr(skb)->daddr))
 				continue;
 #endif
+		} else {
+			continue;
 		}
 
 		if (sk->sk_bound_dev_if && sk->sk_bound_dev_if != dif)