block: brd: associate with queue until adding disk

brd_free() may be called in failure path on one brd instance which
disk isn't added yet, so release handler of gendisk may free the
associated request_queue early and causes the following use-after-free[1].

This patch fixes this issue by associating gendisk with request_queue
just before adding disk.

[1] KASAN: use-after-free Read in del_timer_syncNon-volatile memory driver v1.3
Linux agpgart interface v0.103
[drm] Initialized vgem 1.0.0 20120112 for virtual device on minor 0
usbcore: registered new interface driver udl
==================================================================
BUG: KASAN: use-after-free in __lock_acquire+0x36d9/0x4c20
kernel/locking/lockdep.c:3218
Read of size 8 at addr ffff8801d1b6b540 by task swapper/0/1

CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.0+ #88
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x244/0x39d lib/dump_stack.c:113
  print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
  __lock_acquire+0x36d9/0x4c20 kernel/locking/lockdep.c:3218
  lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844
  del_timer_sync+0xb7/0x270 kernel/time/timer.c:1283
  blk_cleanup_queue+0x413/0x710 block/blk-core.c:809
  brd_free+0x5d/0x71 drivers/block/brd.c:422
  brd_init+0x2eb/0x393 drivers/block/brd.c:518
  do_one_initcall+0x145/0x957 init/main.c:890
  do_initcall_level init/main.c:958 [inline]
  do_initcalls init/main.c:966 [inline]
  do_basic_setup init/main.c:984 [inline]
  kernel_init_freeable+0x5c6/0x6b9 init/main.c:1148
  kernel_init+0x11/0x1ae init/main.c:1068
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:350

Reported-by: syzbot+3701447012fe951dabb2@syzkaller.appspotmail.com
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/brd.c

@@ -396,15 +396,14 @@ static struct brd_device *brd_alloc(int i)
 	disk->first_minor	= i * max_part;
 	disk->fops		= &brd_fops;
 	disk->private_data	= brd;
-	disk->queue		= brd->brd_queue;
 	disk->flags		= GENHD_FL_EXT_DEVT;
 	sprintf(disk->disk_name, "ram%d", i);
 	set_capacity(disk, rd_size * 2);
-	disk->queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO;
+	brd->brd_queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO;
 
 	/* Tell the block layer that this is not a rotational device */
-	blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
-	blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, disk->queue);
+	blk_queue_flag_set(QUEUE_FLAG_NONROT, brd->brd_queue);
+	blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, brd->brd_queue);
 
 	return brd;
 
@@ -436,6 +435,7 @@ static struct brd_device *brd_init_one(int i, bool *new)
 
 	brd = brd_alloc(i);
 	if (brd) {
+		brd->brd_disk->queue = brd->brd_queue;
 		add_disk(brd->brd_disk);
 		list_add_tail(&brd->brd_list, &brd_devices);
 	}
@@ -503,8 +503,14 @@ static int __init brd_init(void)
 
 	/* point of no return */
 
-	list_for_each_entry(brd, &brd_devices, brd_list)
+	list_for_each_entry(brd, &brd_devices, brd_list) {
+		/*
+		 * associate with queue just before adding disk for
+		 * avoiding to mess up failure path
+		 */
+		brd->brd_disk->queue = brd->brd_queue;
 		add_disk(brd->brd_disk);
+	}
 
 	blk_register_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS,
 				  THIS_MODULE, brd_probe, NULL, NULL);