fs, nfsd: convert nfs4_stid.sc_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 nfs4_stid.sc_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: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 86aa92d..c259271c 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -36,6 +36,7 @@
#define _NFSD4_STATE_H
#include <linux/idr.h>
+#include <linux/refcount.h>
#include <linux/sunrpc/svc_xprt.h>
#include "nfsfh.h"
@@ -83,7 +84,7 @@ struct nfsd4_callback_ops {
* fields that are of general use to any stateid.
*/
struct nfs4_stid {
- atomic_t sc_count;
+ refcount_t sc_count;
#define NFS4_OPEN_STID 1
#define NFS4_LOCK_STID 2
#define NFS4_DELEG_STID 4