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 xfs_bui_log_item.bui_refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keesc...@chromium.org>
Reviewed-by: David Windsor <dwind...@gmail.com>
Reviewed-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshet...@intel.com>
---
fs/xfs/xfs_bmap_item.c | 6 +++---
fs/xfs/xfs_bmap_item.h | 2 +-
fs/xfs/xfs_linux.h | 1 +
3 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
index dd136f7..0f2e3d8 100644
--- a/fs/xfs/xfs_bmap_item.c
+++ b/fs/xfs/xfs_bmap_item.c
@@ -201,7 +201,7 @@ xfs_bui_init(
buip->bui_format.bui_nextents = XFS_BUI_MAX_FAST_EXTENTS;
buip->bui_format.bui_id = (uintptr_t)(void *)buip;
atomic_set(&buip->bui_next_extent, 0);
- atomic_set(&buip->bui_refcount, 2);
+ refcount_set(&buip->bui_refcount, 2);
return buip;
}
@@ -217,8 +217,8 @@ void
xfs_bui_release(
struct xfs_bui_log_item *buip)
{
- ASSERT(atomic_read(&buip->bui_refcount) > 0);
- if (atomic_dec_and_test(&buip->bui_refcount)) {
+ ASSERT(refcount_read(&buip->bui_refcount) > 0);
+ if (refcount_dec_and_test(&buip->bui_refcount)) {
xfs_trans_ail_remove(&buip->bui_item, SHUTDOWN_LOG_IO_ERROR);
xfs_bui_item_free(buip);
}
diff --git a/fs/xfs/xfs_bmap_item.h b/fs/xfs/xfs_bmap_item.h
index c867daa..7048b14 100644
--- a/fs/xfs/xfs_bmap_item.h
+++ b/fs/xfs/xfs_bmap_item.h
@@ -61,7 +61,7 @@ struct kmem_zone;
*/
struct xfs_bui_log_item {
struct xfs_log_item bui_item;
- atomic_t bui_refcount;
+ refcount_t bui_refcount;
atomic_t bui_next_extent;
unsigned long bui_flags; /* misc flags */
struct xfs_bui_log_format bui_format;
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index dcd1292..0def85f 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -20,6 +20,7 @@
#include <linux/types.h>
#include <linux/uuid.h>
+#include <linux/refcount.h>
/*
* Kernel specific type declarations for XFS
--
2.7.4
