[PATCH 4/4] fs, afs: convert afs_volume.usage from atomic_t to refcount_t

[Elena Reshetova <elena.reshetova@intel.com>]

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 fs/afs/internal.h | 4 ++--
 fs/afs/volume.c   | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 127567c..8f05daf 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -302,7 +302,7 @@ struct afs_server {
  * AFS volume access record
  */
 struct afs_volume {
-	atomic_t		usage;
+	refcount_t		usage;
 	struct afs_cell		*cell;		/* cell to which belongs (unrefd ptr) */
 	struct afs_vlocation	*vlocation;	/* volume location */
 #ifdef CONFIG_AFS_FSCACHE
@@ -694,7 +694,7 @@ extern int afs_vnode_release_lock(struct afs_vnode *, struct key *);
 /*
  * volume.c
  */
-#define afs_get_volume(V) do { atomic_inc(&(V)->usage); } while(0)
+#define afs_get_volume(V) do { refcount_inc(&(V)->usage); } while(0)
 
 extern void afs_put_volume(struct afs_volume *);
 extern struct afs_volume *afs_volume_lookup(struct afs_mount_params *);
diff --git a/fs/afs/volume.c b/fs/afs/volume.c
index 546f9d0..6590606 100644
--- a/fs/afs/volume.c
+++ b/fs/afs/volume.c
@@ -100,7 +100,7 @@ struct afs_volume *afs_volume_lookup(struct afs_mount_params *params)
 	if (!volume)
 		goto error_up;
 
-	atomic_set(&volume->usage, 1);
+	refcount_set(&volume->usage, 1);
 	volume->type		= params->type;
 	volume->type_force	= params->force;
 	volume->cell		= params->cell;
@@ -180,7 +180,7 @@ void afs_put_volume(struct afs_volume *volume)
 
 	_enter("%p", volume);
 
-	ASSERTCMP(atomic_read(&volume->usage), >, 0);
+	ASSERTCMP(refcount_read(&volume->usage), >, 0);
 
 	vlocation = volume->vlocation;
 
@@ -188,7 +188,7 @@ void afs_put_volume(struct afs_volume *volume)
 	 * atomic */
 	down_write(&vlocation->cell->vl_sem);
 
-	if (likely(!atomic_dec_and_test(&volume->usage))) {
+	if (likely(!refcount_dec_and_test(&volume->usage))) {
 		up_write(&vlocation->cell->vl_sem);
 		_leave("");
 		return;
-- 
2.7.4