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bcache: convert cached_dev.count from atomic_t to refcount_t 

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 cached_dev.count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Elena Reshetova 2017-10-30 14:46:32 -07:00 committed by Jens Axboe
parent d59b237959
commit 3b304d24a7
3 changed files with 8 additions and 7 deletions
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7
drivers/md/bcache/bcache.h
View File

@ -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>
@ -296,7 +297,7 @@ 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 */

6
drivers/md/bcache/super.c
View File

@ -902,7 +902,7 @@ 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);
@ -1029,7 +1029,7 @@ 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);
@ -1041,7 +1041,7 @@ 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->disk);
atomic_set(&dc->has_dirty, 1);
atomic_inc(&dc->count);
refcount_inc(&dc->count);
bch_writeback_queue(dc);
}

2
drivers/md/bcache/writeback.h
View File

@ -91,7 +91,7 @@ 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);