sock.c: potential null dereference

We test that "prot->rsk_prot" is non-null right before we dereference it
on this line.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -2288,7 +2288,8 @@ int proto_register(struct proto *prot, int alloc_slab)
 		prot->rsk_prot->slab = NULL;
 	}
 out_free_request_sock_slab_name:
-	kfree(prot->rsk_prot->slab_name);
+	if (prot->rsk_prot)
+		kfree(prot->rsk_prot->slab_name);
 out_free_sock_slab:
 	kmem_cache_destroy(prot->slab);
 	prot->slab = NULL;