KASAN: null-ptr-deref Write in bdi_put

KASAN: null-ptr-deref Write in bdi_put

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    15ac8fdb Add linux-next specific files for 20201207
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1735927b500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3696b8138207d24d
dashboard link: https://syzkaller.appspot.com/bug?extid=aded2f2ab94d81727898
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11993623500000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15799413500000

The issue was bisected to:

commit 4d004099a668c41522242aa146a38cc4eb59cb1e
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Fri Oct 2 09:04:21 2020 +0000

    lockdep: Fix lockdep recursion

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1469d00f500000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1669d00f500000
console output: https://syzkaller.appspot.com/x/log.txt?x=1269d00f500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aded2f2ab94d81727898@syzkaller.appspotmail.com
Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion")

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: null-ptr-deref in atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
BUG: KASAN: null-ptr-deref in __refcount_sub_and_test include/linux/refcount.h:272 [inline]
BUG: KASAN: null-ptr-deref in __refcount_dec_and_test include/linux/refcount.h:315 [inline]
BUG: KASAN: null-ptr-deref in refcount_dec_and_test include/linux/refcount.h:333 [inline]
BUG: KASAN: null-ptr-deref in kref_put include/linux/kref.h:64 [inline]
BUG: KASAN: null-ptr-deref in bdi_put+0x22/0xa0 mm/backing-dev.c:901
Write of size 4 at addr 0000000000000040 by task syz-executor719/8459

CPU: 1 PID: 8459 Comm: syz-executor719 Not tainted 5.10.0-rc6-next-20201207-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 __kasan_report mm/kasan/report.c:400 [inline]
 kasan_report.cold+0x5f/0xd5 mm/kasan/report.c:413
 check_memory_region_inline mm/kasan/generic.c:180 [inline]
 check_memory_region+0x13d/0x180 mm/kasan/generic.c:186
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
 __refcount_sub_and_test include/linux/refcount.h:272 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 kref_put include/linux/kref.h:64 [inline]
 bdi_put+0x22/0xa0 mm/backing-dev.c:901
 bdev_evict_inode+0x280/0x4a0 fs/block_dev.c:809
 evict+0x2ed/0x6b0 fs/inode.c:577
 iput_final fs/inode.c:1651 [inline]
 iput.part.0+0x41e/0x840 fs/inode.c:1677
 iput+0x58/0x70 fs/inode.c:1667
 dentry_unlink_inode+0x2b1/0x3d0 fs/dcache.c:374
 __dentry_kill+0x3c0/0x640 fs/dcache.c:579
 dentry_kill fs/dcache.c:705 [inline]
 dput+0x786/0xc10 fs/dcache.c:878
 do_one_tree fs/dcache.c:1625 [inline]
 shrink_dcache_for_umount+0x11f/0x330 fs/dcache.c:1639
 generic_shutdown_super+0x68/0x370 fs/super.c:447
 kill_anon_super+0x36/0x60 fs/super.c:1055
 deactivate_locked_super+0x94/0x160 fs/super.c:335
 deactivate_super+0xad/0xd0 fs/super.c:366
 cleanup_mnt+0x3a3/0x530 fs/namespace.c:1123
 task_work_run+0xdd/0x190 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x1f0/0x200 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:302
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x444439
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 db d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc4e2a8a38 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffea RBX: 00007ffc4e2a8a40 RCX: 0000000000444439
RDX: 0000000020000100 RSI: 00000000200000c0 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000400c60
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004020a0
R13: 0000000000402130 R14: 0000000000000000 R15: 0000000000000000
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: KASAN: null-ptr-deref Write in bdi_put

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 2d2f6f1b4799428d160c021dd652bc3e3593945e
Author: Christoph Hellwig <hch@lst.de>
Date:   Thu Jan 7 18:36:40 2021 +0000

    block: pre-initialize struct block_device in bdev_alloc_inode

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1424a5b6d00000
start commit:   71c061d2 Merge tag 'for-5.11-rc2-tag' of git://git.kernel...
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=33b7f56c5bf0f684
dashboard link: https://syzkaller.appspot.com/bug?extid=aded2f2ab94d81727898
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=143f7fc0d00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1089023f500000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: block: pre-initialize struct block_device in bdev_alloc_inode

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: KASAN: null-ptr-deref Write in bdi_put

[Jens Axboe]

On 3/1/21 5:56 AM, syzbot wrote:
> syzbot suspects this issue was fixed by commit:
> 
> commit 2d2f6f1b4799428d160c021dd652bc3e3593945e
> Author: Christoph Hellwig <hch@lst.de>
> Date:   Thu Jan 7 18:36:40 2021 +0000
> 
>     block: pre-initialize struct block_device in bdev_alloc_inode
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1424a5b6d00000
> start commit:   71c061d2 Merge tag 'for-5.11-rc2-tag' of git://git.kernel...
> git tree:       upstream
> kernel config:  https://syzkaller.appspot.com/x/.config?x=33b7f56c5bf0f684
> dashboard link: https://syzkaller.appspot.com/bug?extid=aded2f2ab94d81727898
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=143f7fc0d00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1089023f500000
> 
> If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: block: pre-initialize struct block_device in bdev_alloc_inode


-- 
Jens Axboe