net: avoid NULL deref in inet_ctl_sock_destroy()

[ Upstream commit 8fa677d2 ]

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@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

include/net/inet_common.h

@@ -42,7 +42,8 @@ int inet_recv_error(struct sock *sk, struct msghdr *msg, int len,
 
 static inline void inet_ctl_sock_destroy(struct sock *sk)
 {
-	sk_release_kernel(sk);
+	if (sk)
+		sk_release_kernel(sk);
 }
 
 #endif