[PATCH 4/5] block: convert io_context.active_ref from atomic_t to refcount_t

Elena Reshetova
2017-04-20T11:28:05Z

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@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
block/blk-ioc.c | 4 ++--
block/cfq-iosched.c | 4 ++--
include/linux/iocontext.h | 6 +++---
3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index b12f9c8..130dc23 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -173,7 +173,7 @@ 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;
}
@@ -256,7 +256,7 @@ 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 9212627..2871bb9 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2959,7 +2959,7 @@ 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;

/*
@@ -3959,7 +3959,7 @@ 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..e47b907 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 +129,8 @@ 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);
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