[PATCH 05/29] drivers, md, bcache: convert cached_dev.count from atomic_t to refcount_t

Elena Reshetova
2017-03-06T14:20:52Z

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>
---
drivers/md/bcache/bcache.h | 7 ++++---
drivers/md/bcache/super.c | 6 +++---
drivers/md/bcache/writeback.h | 2 +-
3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index c3ea03c..de2be28 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -184,6 +184,7 @@
#include <linux/mutex.h>
#include <linux/rbtree.h>
#include <linux/rwsem.h>
+#include <linux/refcount.h>
#include <linux/types.h>
#include <linux/workqueue.h>

@@ -299,7 +300,7 @@ struct cached_dev {
struct semaphore sb_write_mutex;

/* Refcount on the cache set. Always nonzero when we're caching. */
- atomic_t count;
+ refcount_t count;
struct work_struct detach;

/*
@@ -805,13 +806,13 @@ do { \

static inline void cached_dev_put(struct cached_dev *dc)
{
- if (atomic_dec_and_test(&dc->count))
+ if (refcount_dec_and_test(&dc->count))
schedule_work(&dc->detach);
}

static inline bool cached_dev_get(struct cached_dev *dc)
{
- if (!atomic_inc_not_zero(&dc->count))
+ if (!refcount_inc_not_zero(&dc->count))
return false;

/* Paired with the mb in cached_dev_attach */
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 85e3f21..cc36ce4 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -891,7 +891,7 @@ static void cached_dev_detach_finish(struct work_struct *w)
closure_init_stack(&cl);

BUG_ON(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags));
- BUG_ON(atomic_read(&dc->count));
+ BUG_ON(refcount_read(&dc->count));

mutex_lock(&bch_register_lock);

@@ -1018,7 +1018,7 @@ int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c)
* dc->c must be set before dc->count != 0 - paired with the mb in
* cached_dev_get()
*/
- atomic_set(&dc->count, 1);
+ refcount_set(&dc->count, 1);

/* Block writeback thread, but spawn it */
down_write(&dc->writeback_lock);
@@ -1030,7 +1030,7 @@ int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c)
if (BDEV_STATE(&dc->sb) == BDEV_STATE_DIRTY) {
bch_sectors_dirty_init(dc);
atomic_set(&dc->has_dirty, 1);
- atomic_inc(&dc->count);
+ refcount_inc(&dc->count);
bch_writeback_queue(dc);
}

diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index 629bd1a..5bac1b0 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -70,7 +70,7 @@ static inline void bch_writeback_add(struct cached_dev *dc)
{
if (!atomic_read(&dc->has_dirty) &&
!atomic_xchg(&dc->has_dirty, 1)) {
- atomic_inc(&dc->count);
+ refcount_inc(&dc->count);

if (BDEV_STATE(&dc->sb) != BDEV_STATE_DIRTY) {
SET_BDEV_STATE(&dc->sb, BDEV_STATE_DIRTY);
--
2.7.4