sock: fix potential memory leak in proto_register()

If protocols registered exceeded PROTO_INUSE_NR, prot will be
added to proto_list, but no available bit left for prot in
proto_inuse_idx.

Changes since v2:
* Propagate the error code properly
Signed-off-by: Nzhanglin <zhang.lin16@zte.com.cn>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -3287,16 +3287,17 @@ static __init int net_inuse_init(void)
 
 core_initcall(net_inuse_init);
 
-static void assign_proto_idx(struct proto *prot)
+static int assign_proto_idx(struct proto *prot)
 {
 	prot->inuse_idx = find_first_zero_bit(proto_inuse_idx, PROTO_INUSE_NR);
 
 	if (unlikely(prot->inuse_idx == PROTO_INUSE_NR - 1)) {
 		pr_err("PROTO_INUSE_NR exhausted\n");
-		return;
+		return -ENOSPC;
 	}
 
 	set_bit(prot->inuse_idx, proto_inuse_idx);
+	return 0;
 }
 
 static void release_proto_idx(struct proto *prot)
@@ -3305,8 +3306,9 @@ static void release_proto_idx(struct proto *prot)
 		clear_bit(prot->inuse_idx, proto_inuse_idx);
 }
 #else
-static inline void assign_proto_idx(struct proto *prot)
+static inline int assign_proto_idx(struct proto *prot)
 {
+	return 0;
 }
 
 static inline void release_proto_idx(struct proto *prot)
@@ -3355,6 +3357,8 @@ static int req_prot_init(const struct proto *prot)
 
 int proto_register(struct proto *prot, int alloc_slab)
 {
+	int ret = -ENOBUFS;
+
 	if (alloc_slab) {
 		prot->slab = kmem_cache_create_usercopy(prot->name,
 					prot->obj_size, 0,
@@ -3391,20 +3395,27 @@ int proto_register(struct proto *prot, int alloc_slab)
 	}
 
 	mutex_lock(&proto_list_mutex);
+	ret = assign_proto_idx(prot);
+	if (ret) {
+		mutex_unlock(&proto_list_mutex);
+		goto out_free_timewait_sock_slab_name;
+	}
 	list_add(&prot->node, &proto_list);
-	assign_proto_idx(prot);
 	mutex_unlock(&proto_list_mutex);
-	return 0;
+	return ret;
 
 out_free_timewait_sock_slab_name:
-	kfree(prot->twsk_prot->twsk_slab_name);
+	if (alloc_slab && prot->twsk_prot)
+		kfree(prot->twsk_prot->twsk_slab_name);
 out_free_request_sock_slab:
-	req_prot_cleanup(prot->rsk_prot);
+	if (alloc_slab) {
+		req_prot_cleanup(prot->rsk_prot);
 
-	kmem_cache_destroy(prot->slab);
-	prot->slab = NULL;
+		kmem_cache_destroy(prot->slab);
+		prot->slab = NULL;
+	}
 out:
-	return -ENOBUFS;
+	return ret;
 }
 EXPORT_SYMBOL(proto_register);