blk-mq: Do not invoke queue operations on a dead queue

In commit e869b5462f83 ("blk-mq: Unregister debugfs attributes
earlier"), we shuffled the debugfs cleanup around so that the "state"
attribute was removed before we freed the blk-mq data structures.
However, later changes are going to undo that, so we need to explicitly
disallow running a dead queue.

[Omar: rebased and updated commit message]
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 1579af6fcbed..347fbb8e059c 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -102,6 +102,14 @@ static ssize_t queue_state_write(void *data, const char __user *buf,
         struct request_queue *q = data;
         char opbuf[16] = { }, *op;
 
+        /*
+         * The "state" attribute is removed after blk_cleanup_queue() has called
+         * blk_mq_free_queue(). Return if QUEUE_FLAG_DEAD has been set to avoid
+         * triggering a use-after-free.
+         */
+        if (blk_queue_dead(q))
+                return -ENOENT;
+
         if (count >= sizeof(opbuf)) {
                 pr_err("%s: operation too long\n", __func__);
                 goto inval;