[PATCH 3.16.y-ckt 011/126] net: avoid NULL deref in inet_ctl_sock_destroy()

[Luis Henriques]

3.16.7-ckt21 -stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet at google.com>

commit 8fa677d2706d325d71dab91bf6e6512c05214e37 upstream.

Under low memory conditions, tcp_sk_init() and icmp_sk_init()
can both iterate on all possible cpus and call inet_ctl_sock_destroy(),
with eventual NULL pointer.

Signed-off-by: Eric Dumazet <edumazet at google.com>
Reported-by: Dmitry Vyukov <dvyukov at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 include/net/inet_common.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/net/inet_common.h b/include/net/inet_common.h
index fe7994c48b75..fd1da045dabc 100644
--- a/include/net/inet_common.h
+++ b/include/net/inet_common.h
@@ -40,7 +40,8 @@ int inet_ctl_sock_create(struct sock **sk, unsigned short family,
 
 static inline void inet_ctl_sock_destroy(struct sock *sk)
 {
-	sk_release_kernel(sk);
+	if (sk)
+		sk_release_kernel(sk);
 }
 
 #endif