From 3b304d24a718ae779ee9c7f2014dd3b2d0893b70 Mon Sep 17 00:00:00 2001 From: Elena Reshetova Date: Mon, 30 Oct 2017 14:46:32 -0700 Subject: [PATCH] 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 Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Reviewed-by: Michael Lyle Signed-off-by: Elena Reshetova Signed-off-by: Jens Axboe --- 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 d77c4829c497..363ea6256b39 100644 --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -184,6 +184,7 @@ #include #include #include +#include #include #include @@ -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 */ diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 72c3b2929ef0..46134c45c6f6 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -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); } diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h index 34bcf49d737b..7d25bff37a9b 100644 --- a/drivers/md/bcache/writeback.h +++ b/drivers/md/bcache/writeback.h @@ -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); -- 2.11.0