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 io_context.active_ref 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>
---
block/bfq-iosched.c | 2 +-
block/blk-ioc.c | 4 ++--
block/cfq-iosched.c | 4 ++--
include/linux/iocontext.h | 7 ++++---
4 files changed, 9 insertions(+), 8 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index a4783da..1ec9b22 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4030,7 +4030,7 @@ static void bfq_update_has_short_ttime(struct bfq_data
*bfqd,
* bfqq. Otherwise check average think time to
* decide whether to mark as has_short_ttime
*/
- if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
+ if (refcount_read(&bic->icq.ioc->active_ref) == 0 ||
(bfq_sample_valid(bfqq->ttime.ttime_samples) &&
bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle))
has_short_ttime = false;
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 63898d2..69704d2 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -176,7 +176,7 @@ void put_io_context_active(struct io_context *ioc)
unsigned long flags;
struct io_cq *icq;
- if (!atomic_dec_and_test(&ioc->active_ref)) {
+ if (!refcount_dec_and_test(&ioc->active_ref)) {
put_io_context(ioc);
return;
}
@@ -275,7 +275,7 @@ int create_task_io_context(struct task_struct *task, gfp_t
gfp_flags, int node)
/* initialize */
atomic_long_set(&ioc->refcount, 1);
atomic_set(&ioc->nr_tasks, 1);
- atomic_set(&ioc->active_ref, 1);
+ refcount_set(&ioc->active_ref, 1);
spin_lock_init(&ioc->lock);
INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
INIT_HLIST_HEAD(&ioc->icq_list);
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9f342ef..e6d5d6d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2941,7 +2941,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
* task has exited, don't wait
*/
cic = cfqd->active_cic;
- if (!cic || !atomic_read(&cic->icq.ioc->active_ref))
+ if (!cic || !refcount_read(&cic->icq.ioc->active_ref))
return;
/*
@@ -3933,7 +3933,7 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct
cfq_queue *cfqq,
if (cfqq->next_rq && req_noidle(cfqq->next_rq))
enable_idle = 0;
- else if (!atomic_read(&cic->icq.ioc->active_ref) ||
+ else if (!refcount_read(&cic->icq.ioc->active_ref) ||
!cfqd->cfq_slice_idle ||
(!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
enable_idle = 0;
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index df38db2..a1e28c3 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -3,6 +3,7 @@
#include <linux/radix-tree.h>
#include <linux/rcupdate.h>
+#include <linux/refcount.h>
#include <linux/workqueue.h>
enum {
@@ -96,7 +97,7 @@ struct io_cq {
*/
struct io_context {
atomic_long_t refcount;
- atomic_t active_ref;
+ refcount_t active_ref;
atomic_t nr_tasks;
/* all the fields below are protected by this lock */
@@ -128,9 +129,9 @@ struct io_context {
static inline void get_io_context_active(struct io_context *ioc)
{
WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
- WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
+ WARN_ON_ONCE(refcount_read(&ioc->active_ref) == 0);
atomic_long_inc(&ioc->refcount);
- atomic_inc(&ioc->active_ref);
+ refcount_inc(&ioc->active_ref);
}
static inline void ioc_task_link(struct io_context *ioc)
--
2.7.4
