Re: upstream boot error (2)

[Ming Lei <ming.lei@redhat.com>]

On Tue, Oct 30, 2018 at 08:00:04AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    11743c56785c Merge tag 'rpmsg-v4.20' of git://github.com/a..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15121199400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=93932074d01b4a5
> dashboard link: https://syzkaller.appspot.com/bug?extid=3701447012fe951dabb2
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+3701447012fe951dabb2@syzkaller.appspotmail.com
> 
> 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
> 
> Allocated by task 1:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
>  kmem_cache_alloc_node_trace+0x14c/0x740 mm/slab.c:3663
>  kmalloc_node include/linux/slab.h:584 [inline]
>  bdi_alloc_node+0x89/0xe0 mm/backing-dev.c:861
>  blk_alloc_queue_node+0x2b7/0xe80 block/blk-core.c:1024
>  blk_alloc_queue+0x1a/0x20 block/blk-core.c:911
>  brd_alloc+0xb9/0x540 drivers/block/brd.c:378
>  brd_init+0x11d/0x393 drivers/block/brd.c:498
>  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
> 
> Freed by task 12:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kfree+0xcf/0x230 mm/slab.c:3817
>  release_bdi mm/backing-dev.c:968 [inline]
>  kref_put include/linux/kref.h:70 [inline]
>  bdi_put+0x138/0x180 mm/backing-dev.c:973
>  blk_exit_queue+0xbf/0xf0 block/blk-core.c:746
>  __blk_release_queue+0x12f/0x510 block/blk-sysfs.c:841
>  process_one_work+0xc90/0x1c40 kernel/workqueue.c:2153
>  worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
>  kthread+0x35a/0x440 kernel/kthread.c:246
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:350
> 
> The buggy address belongs to the object at ffff8801d1b6ae80
>  which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 1728 bytes inside of
>  2048-byte region [ffff8801d1b6ae80, ffff8801d1b6b680)
> The buggy address belongs to the page:
> page:ffffea000746da80 count:1 mapcount:0 mapping:ffff8801da800c40 index:0x0
> compound_mapcount: 0
> flags: 0x2fffc0000010200(slab|head)
> raw: 02fffc0000010200 ffffea000746da08 ffffea000746dc08 ffff8801da800c40
> raw: 0000000000000000 ffff8801d1b6a600 0000000100000003 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801d1b6b400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801d1b6b480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8801d1b6b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                            ^
>  ffff8801d1b6b580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801d1b6b600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 

This issue should have been fixed by the following one-line change:

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index df8103dd40ac..a5ecff2071ce 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -515,6 +515,8 @@ static int __init brd_init(void)
 out_free:
 	list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
 		list_del(&brd->brd_list);
+		/* don't let put_disk() drop the queue's ref */
+		brd->brd_disk->queue = NULL;
 		brd_free(brd);
 	}
 	unregister_blkdev(RAMDISK_MAJOR, "ramdisk");

-- 
Ming