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>
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 74c4466..efcfe9d 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -9,6 +9,7 @@
#include <linux/sunrpc/xprt.h>
#include <linux/atomic.h>
+#include <linux/refcount.h>
struct nfs4_session;
struct nfs_iostats;
@@ -24,7 +25,7 @@ struct nfs41_impl_id;
* The nfs_client identifies our client state to the server.
*/
struct nfs_client {
- atomic_t cl_count;
+ refcount_t cl_count;
atomic_t cl_mds_count;
int cl_cons_state; /* current construction state (-ve: init error) */
#define NFS_CS_READY 0 /* ready to be used */