block: fix use-after-free bug in blk throttle code

blk_throtl_exit() frees the throttle data hanging off the queue
in blk_cleanup_queue(), but blk_put_queue() will indirectly
dereference this data when calling blk_sync_queue() which in
turns calls throtl_shutdown_timer_wq().

Fix this by moving the freeing of the throttle data to when
the queue is truly being released, and post the call to
blk_sync_queue().

Reported-by: Ingo Molnar <mingo@elte.hu>
Tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

2 files changed, 2 insertions, 2 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 45141469e89e..51efd835d4cf 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -462,8 +462,6 @@ void blk_cleanup_queue(struct request_queue *q)
         if (q->elevator)
                 elevator_exit(q->elevator);
 
-        blk_throtl_exit(q);
-
         blk_put_queue(q);
 }
 EXPORT_SYMBOL(blk_cleanup_queue);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index da8a8a40cd4c..013457f47fdc 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -471,6 +471,8 @@ static void blk_release_queue(struct kobject *kobj)
 
         blk_sync_queue(q);
 
+        blk_throtl_exit(q);
+
         if (rl->rq_pool)
                 mempool_destroy(rl->rq_pool);