[PATCH 1/2] ubi: block: Fix use-after-free of gendisk

[Vincent Whitchurch]

Do not touch the gendisk after put_disk() to fix this use-after-free:

 ==================================================
 BUG: KASAN: slab-use-after-free in ubiblock_remove
 Read of size 4 by task ubiblock/361

 Call Trace:
 ubiblock_remove (drivers/mtd/ubi/block.c:459 drivers/mtd/ubi/block.c:483)
 vol_cdev_ioctl
 ...

 Allocated by task 358:
 __alloc_disk_node (block/genhd.c:1377)
 __blk_mq_alloc_disk (block/blk-mq.c:4093)
 ubiblock_create (drivers/mtd/ubi/block.c:397)
 vol_cdev_ioctl
 ...

 Freed by task 0:
 bdev_free_inode (block/bdev.c:337)
 i_callback
 rcu_core
 __do_softirq
 ...

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
---
 drivers/mtd/ubi/block.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
index 3711d7f74600..70caec4606cd 100644
--- a/drivers/mtd/ubi/block.c
+++ b/drivers/mtd/ubi/block.c
@@ -448,13 +448,15 @@ int ubiblock_create(struct ubi_volume_info *vi)
 
 static void ubiblock_cleanup(struct ubiblock *dev)
 {
+	int first_minor = dev->gd->first_minor;
+
 	/* Stop new requests to arrive */
 	del_gendisk(dev->gd);
 	/* Finally destroy the blk queue */
 	dev_info(disk_to_dev(dev->gd), "released");
 	put_disk(dev->gd);
 	blk_mq_free_tag_set(&dev->tag_set);
-	idr_remove(&ubiblock_minor_idr, dev->gd->first_minor);
+	idr_remove(&ubiblock_minor_idr, first_minor);
 }
 
 int ubiblock_remove(struct ubi_volume_info *vi)

-- 
2.34.1