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 xlog_ticket.t_ref is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
fs/xfs/xfs_log.c | 10 +++++-----
fs/xfs/xfs_log_priv.h | 2 +-
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index dc95a49..e4578c0 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3571,8 +3571,8 @@ void
xfs_log_ticket_put(
xlog_ticket_t *ticket)
{
- ASSERT(atomic_read(&ticket->t_ref) > 0);
- if (atomic_dec_and_test(&ticket->t_ref))
+ ASSERT(refcount_read(&ticket->t_ref) > 0);
+ if (refcount_dec_and_test(&ticket->t_ref))
kmem_zone_free(xfs_log_ticket_zone, ticket);
}
@@ -3580,8 +3580,8 @@ xlog_ticket_t *
xfs_log_ticket_get(
xlog_ticket_t *ticket)
{
- ASSERT(atomic_read(&ticket->t_ref) > 0);
- atomic_inc(&ticket->t_ref);
+ ASSERT(refcount_read(&ticket->t_ref) > 0);
+ refcount_inc(&ticket->t_ref);
return ticket;
}
@@ -3703,7 +3703,7 @@ xlog_ticket_alloc(
unit_res = xfs_log_calc_unit_res(log->l_mp, unit_bytes);
- atomic_set(&tic->t_ref, 1);
+ refcount_set(&tic->t_ref, 1);
tic->t_task = current;
INIT_LIST_HEAD(&tic->t_queue);
tic->t_unit_res = unit_res;
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 51bf7b8..29f6e1f 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -168,7 +168,7 @@ typedef struct xlog_ticket {
struct list_head t_queue; /* reserve/write queue */
struct task_struct *t_task; /* task that owns this ticket */
xlog_tid_t t_tid; /* transaction identifier : 4 */
- atomic_t t_ref; /* ticket reference count : 4 */
+ refcount_t t_ref; /* ticket reference count : 4 */
int t_curr_res; /* current reservation in bytes : 4 */
int t_unit_res; /* unit reservation in bytes : 4 */
char t_ocnt; /* original count : 1 */
--
2.7.4
--
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