[PATCH 2/5] fs, xfs: convert xfs_efi_log_item.efi_refcount from atomic_t to refcount_t

[Elena Reshetova]

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@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 fs/xfs/xfs_extfree_item.c | 4 ++--
 fs/xfs/xfs_extfree_item.h | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c
index d7bc149..4e0acf0 100644
--- a/fs/xfs/xfs_extfree_item.c
+++ b/fs/xfs/xfs_extfree_item.c
@@ -220,7 +220,7 @@ xfs_efi_init(
 	efip->efi_format.efi_nextents = nextents;
 	efip->efi_format.efi_id = (uintptr_t)(void *)efip;
 	atomic_set(&efip->efi_next_extent, 0);
-	atomic_set(&efip->efi_refcount, 2);
+	refcount_set(&efip->efi_refcount, 2);
 
 	return efip;
 }
@@ -290,7 +290,7 @@ void
 xfs_efi_release(
 	struct xfs_efi_log_item	*efip)
 {
-	if (atomic_dec_and_test(&efip->efi_refcount)) {
+	if (refcount_dec_and_test(&efip->efi_refcount)) {
 		xfs_trans_ail_remove(&efip->efi_item, SHUTDOWN_LOG_IO_ERROR);
 		xfs_efi_item_free(efip);
 	}
diff --git a/fs/xfs/xfs_extfree_item.h b/fs/xfs/xfs_extfree_item.h
index a32c794..e6da63d 100644
--- a/fs/xfs/xfs_extfree_item.h
+++ b/fs/xfs/xfs_extfree_item.h
@@ -18,6 +18,8 @@
 #ifndef	__XFS_EXTFREE_ITEM_H__
 #define	__XFS_EXTFREE_ITEM_H__
 
+#include <linux/refcount.h>
+
 /* kernel only EFI/EFD definitions */
 
 struct xfs_mount;
@@ -64,7 +66,7 @@ struct kmem_zone;
  */
 typedef struct xfs_efi_log_item {
 	xfs_log_item_t		efi_item;
-	atomic_t		efi_refcount;
+	refcount_t		efi_refcount;
 	atomic_t		efi_next_extent;
 	unsigned long		efi_flags;	/* misc flags */
 	xfs_efi_log_format_t	efi_format;
-- 
2.7.4