fs, nfs: convert nfs_client.cl_count from atomic_t to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable nfs_client.cl_count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 22880ef..0ac2fb1 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -163,7 +163,7 @@ struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_init)
 
 	clp->rpc_ops = clp->cl_nfs_mod->rpc_ops;
 
-	atomic_set(&clp->cl_count, 1);
+	refcount_set(&clp->cl_count, 1);
 	clp->cl_cons_state = NFS_CS_INITING;
 
 	memcpy(&clp->cl_addr, cl_init->addr, cl_init->addrlen);
@@ -269,7 +269,7 @@ void nfs_put_client(struct nfs_client *clp)
 
 	nn = net_generic(clp->cl_net, nfs_net_id);
 
-	if (atomic_dec_and_lock(&clp->cl_count, &nn->nfs_client_lock)) {
+	if (refcount_dec_and_lock(&clp->cl_count, &nn->nfs_client_lock)) {
 		list_del(&clp->cl_share_link);
 		nfs_cb_idr_remove_locked(clp);
 		spin_unlock(&nn->nfs_client_lock);
@@ -314,7 +314,7 @@ static struct nfs_client *nfs_match_client(const struct nfs_client_initdata *dat
 							   sap))
 				continue;
 
-		atomic_inc(&clp->cl_count);
+		refcount_inc(&clp->cl_count);
 		return clp;
 	}
 	return NULL;
@@ -1006,7 +1006,7 @@ struct nfs_server *nfs_clone_server(struct nfs_server *source,
 	/* Copy data from the source */
 	server->nfs_client = source->nfs_client;
 	server->destroy = source->destroy;
-	atomic_inc(&server->nfs_client->cl_count);
+	refcount_inc(&server->nfs_client->cl_count);
 	nfs_server_copy_userdata(server, source);
 
 	server->fsid = fattr->fsid;
@@ -1166,7 +1166,7 @@ static int nfs_server_list_show(struct seq_file *m, void *v)
 		   clp->rpc_ops->version,
 		   rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_HEX_ADDR),
 		   rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_HEX_PORT),
-		   atomic_read(&clp->cl_count),
+		   refcount_read(&clp->cl_count),
 		   clp->cl_hostname);
 	rcu_read_unlock();