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_efi_log_item.efi_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_extfree_item.c | 6 +++---
fs/xfs/xfs_extfree_item.h | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c
index 44f8c54..dfe2bcb 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;
}
@@ -290,8 +290,8 @@ void
xfs_efi_release(
struct xfs_efi_log_item *efip)
{
- ASSERT(atomic_read(&efip->efi_refcount) > 0);
- if (atomic_dec_and_test(&efip->efi_refcount)) {
+ ASSERT(refcount_read(&efip->efi_refcount) > 0);
+ 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..fadf736 100644
--- a/fs/xfs/xfs_extfree_item.h
+++ b/fs/xfs/xfs_extfree_item.h
@@ -64,7 +64,7 @@ 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
