KASAN: slab-out-of-bounds Read in btrfs_scan_one_device

Status: fixed on 2021/03/10 01:48
Subsystems: btrfs
[Documentation on labels]
Fix commit: 0697d9a61099 btrfs: don't access possibly stale fs_info data for printing duplicate device
First crash: 1321d, last: 1321d
Cause bisection: introduced by (bisect log) :
commit 3831bf0094abed51e71cbeca8b6edf8b88c2644b
Author: Johannes Thumshirn <>
Date: Mon Oct 7 09:11:02 2019 +0000

  btrfs: add sha256 to checksumming algorithm

Crash: KASAN: use-after-free Read in btrfs_scan_one_device (log)
Repro: C syz .config
Fix bisection: fixed by (bisect log) :
commit 0697d9a610998b8bdee6b2390836cb2391d8fd1a
Author: Johannes Thumshirn <>
Date: Wed Nov 18 09:03:26 2020 +0000

  btrfs: don't access possibly stale fs_info data for printing duplicate device

Discussions (1)
Title Replies (including bot) Last reply
KASAN: slab-out-of-bounds Read in btrfs_scan_one_device 1 (3) 2020/12/07 09:50

Sample crash report:
BUG: KASAN: slab-out-of-bounds in btrfs_printk+0x421/0x46b fs/btrfs/super.c:245
Read of size 8 at addr ffff8880146246a0 by task systemd-udevd/8518

CPU: 0 PID: 8518 Comm: systemd-udevd Not tainted 5.10.0-rc2-syzkaller #0
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+0x137/0x1be lib/dump_stack.c:118
 print_address_description+0x6c/0x660 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report+0x136/0x1e0 mm/kasan/report.c:562
 btrfs_printk+0x421/0x46b fs/btrfs/super.c:245
 device_list_add+0x1a94/0x1d60 fs/btrfs/volumes.c:943
 btrfs_scan_one_device+0x2e1/0x460 fs/btrfs/volumes.c:1366
 btrfs_control_ioctl+0xd1/0x210 fs/btrfs/super.c:2327
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
RIP: 0033:0x7f7f94bc0017
Code: 00 00 00 48 8b 05 81 7e 2b 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 51 7e 2b 00 f7 d8 64 89 01 48
RSP: 002b:00007ffc3c7245f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f7f94bc0017
RDX: 00007ffc3c724610 RSI: 0000000090009427 RDI: 000000000000000f
RBP: 00007ffc3c724610 R08: 0000000000000000 R09: 0000000000000018
R10: 0000000000000001 R11: 0000000000000246 R12: 000000000000000f
R13: 0000000000000000 R14: 0000564c3b1752c0 R15: 0000564c3b162060

Allocated by task 8745:
 kasan_save_stack mm/kasan/common.c:48 [inline]
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc+0x111/0x140 mm/kasan/common.c:461
 slab_post_alloc_hook+0x3e/0x2b0 mm/slab.h:526
 slab_alloc_node mm/slub.c:2891 [inline]
 kmem_cache_alloc_node+0x144/0x280 mm/slub.c:2927
 alloc_unbound_pwq+0x591/0x1060 kernel/workqueue.c:3801
 apply_wqattrs_prepare+0x3d2/0xcb0 kernel/workqueue.c:3946
 apply_workqueue_attrs_locked+0xcd/0x7b0 kernel/workqueue.c:4029
 apply_workqueue_attrs kernel/workqueue.c:4066 [inline]
 alloc_and_link_pwqs kernel/workqueue.c:4190 [inline]
 alloc_workqueue+0xe7e/0x1480 kernel/workqueue.c:4298
 __btrfs_alloc_workqueue+0x181/0x2d0 fs/btrfs/async-thread.c:108
 btrfs_alloc_workqueue+0x8c/0x1b0 fs/btrfs/async-thread.c:140
 btrfs_init_workqueues fs/btrfs/disk-io.c:2162 [inline]
 open_ctree+0x1243/0x3b3b fs/btrfs/disk-io.c:3088
 btrfs_fill_super fs/btrfs/super.c:1316 [inline]
 btrfs_mount_root+0x9b8/0xb60 fs/btrfs/super.c:1672
 legacy_get_tree+0xea/0x180 fs/fs_context.c:592
 vfs_get_tree+0x88/0x270 fs/super.c:1549
 fc_mount fs/namespace.c:978 [inline]
 vfs_kern_mount+0xc9/0x160 fs/namespace.c:1008
 btrfs_mount+0x345/0xa80 fs/btrfs/super.c:1732
 legacy_get_tree+0xea/0x180 fs/fs_context.c:592
 vfs_get_tree+0x88/0x270 fs/super.c:1549
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x17b4/0x2a20 fs/namespace.c:3205
 do_mount fs/namespace.c:3218 [inline]
 __do_sys_mount fs/namespace.c:3426 [inline]
 __se_sys_mount+0x28c/0x320 fs/namespace.c:3403
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46

The buggy address belongs to the object at ffff888014624400
 which belongs to the cache pool_workqueue of size 512
The buggy address is located 160 bytes to the right of
 512-byte region [ffff888014624400, ffff888014624600)
The buggy address belongs to the page:
page:000000006b59311c refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x14624
head:000000006b59311c order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff88801044dc80
raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888014624580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888014624600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888014624680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888014624700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888014624780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2020/11/06 09:17 upstream 521b619acdc8 64069d48 .config console log report syz C ci-upstream-kasan-gce-smack-root
* Struck through repros no longer work on HEAD.