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

[Elena Reshetova <elena.reshetova@xxxxxxxxx>]

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@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 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


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