fs, nfs: convert nfs4_ff_layout_mirror.ref 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_ff_layout_mirror.ref 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/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
index 98b34c9..ca35426 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -13,6 +13,7 @@
#define FF_FLAGS_NO_IO_THRU_MDS 2
#define FF_FLAGS_NO_READ_IO 4
+#include <linux/refcount.h>
#include "../pnfs.h"
/* XXX: Let's filter out insanely large mirror count for now to avoid oom
@@ -81,7 +82,7 @@ struct nfs4_ff_layout_mirror {
nfs4_stateid stateid;
struct rpc_cred __rcu *ro_cred;
struct rpc_cred __rcu *rw_cred;
- atomic_t ref;
+ refcount_t ref;
spinlock_t lock;
unsigned long flags;
struct nfs4_ff_layoutstat read_stat;