[syzbot] [hfs?] WARNING in hfs_mdb_commit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1bfaee9d3351 Merge tag 'fsverity-for-linus' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12f08726580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7f195f6be48c12ec
dashboard link: https://syzkaller.appspot.com/bug?extid=c149ad75e9633be0c1ad
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-1bfaee9d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/879fc4fe312e/vmlinux-1bfaee9d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9e35bd667fed/bzImage-1bfaee9d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c149ad...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 64
loop0: detected capacity change from 64 to 0
Buffer I/O error on dev loop0, logical block 62, lost sync page write
hfs: unable to read volume bitmap
------------[ cut here ]------------
!buffer_uptodate(bh)
WARNING: fs/buffer.c:1087 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:1087, CPU#0: syz.0.0/5321
Modules linked in:
CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:mark_buffer_dirty+0x299/0x410 fs/buffer.c:1087
Code: 4c 89 f7 e8 b9 5c da ff 49 8b 3e be 40 00 00 00 5b 41 5c 41 5e 41 5f 5d e9 b4 63 fb ff e8 3f 91 6d ff eb 8c e8 38 91 6d ff 90 <0f> 0b 90 e9 a5 fd ff ff e8 2a 91 6d ff 90 0f 0b 90 e9 cf fd ff ff
RSP: 0018:ffffc9000ddafba8 EFLAGS: 00010283
RAX: ffffffff82584008 RBX: ffff888046e26658 RCX: 0000000000100000
RDX: ffffc9000eefa000 RSI: 0000000000001912 RDI: 0000000000001913
RBP: 1ffff11007a3ec01 R08: ffff888046e2665f R09: 1ffff11008dc4ccb
R10: dffffc0000000000 R11: ffffed1008dc4ccc R12: dffffc0000000000
R13: ffff88803d1f6628 R14: ffff888055813c0b R15: ffff888055831492
FS: 00007f2c9e9b96c0(0000) GS:ffff88808c881000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000210 CR3: 00000000133b8000 CR4: 0000000000352ef0
Call Trace:
<TASK>
hfs_mdb_commit+0x84b/0x1150 fs/hfs/mdb.c:328
hfs_sync_fs+0x1d/0x30 fs/hfs/super.c:38
sync_filesystem+0x1cf/0x230 fs/sync.c:66
hfs_reconfigure+0x66/0x270 fs/hfs/super.c:122
reconfigure_super+0x227/0x8a0 fs/super.c:1080
do_remount fs/namespace.c:3400 [inline]
path_mount+0xdc5/0x10e0 fs/namespace.c:4146
do_mount fs/namespace.c:4167 [inline]
__do_sys_mount fs/namespace.c:4383 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4360
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2c9db9cdd9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f2c9e9b8fe8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f2c9de15fa0 RCX: 00007f2c9db9cdd9
RDX: 0000000000000000 RSI: 00002000000002c0 RDI: 0000000000000000
RBP: 00007f2c9dc32d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000c22 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2c9de16038 R14: 00007f2c9de15fa0 R15: 00007fffa4666ff8
</TASK>


---
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[Viacheslav Dubeyko]

On Wed, 2026-05-13 at 20:37 -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 1bfaee9d3351 Merge tag 'fsverity-for-linus' of git://git.k..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12f08726580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=7f195f6be48c12ec
> dashboard link: https://syzkaller.appspot.com/bug?extid=c149ad75e9633be0c1ad
> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
>
> Unfortunately, I don't have any reproducer for this issue yet.
>

It is really sad that we don't have a reproducer for the issue.

> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-1bfaee9d.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/879fc4fe312e/vmlinux-1bfaee9d.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9e35bd667fed/bzImage-1bfaee9d.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+c149ad...@syzkaller.appspotmail.com
>
> loop0: detected capacity change from 0 to 64
> loop0: detected capacity change from 64 to 0
> Buffer I/O error on dev loop0, logical block 62, lost sync page write
> hfs: unable to read volume bitmap

I assume that we have two issues here. As far as I can see, we have 64 blocks in
the HFS volume. And we try to read logical block 62 that expected to have
portion of volume bitmap. Somehow, we've failed to read it:

while (size) {
bh = sb_bread(sb, block);
if (!bh) {
pr_err("unable to read volume bitmap\n");
break;
}
<skipped>
}

And it is not completely clear why the read has failed.

> ------------[ cut here ]------------
> !buffer_uptodate(bh)
> WARNING: fs/buffer.c:1087 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:1087, CPU#0: syz.0.0/5321

But this issue took place because buffer with alternative/backup MDB has not
been set as uptodate:

void mark_buffer_dirty(struct buffer_head *bh)
{
WARN_ON_ONCE(!buffer_uptodate(bh));
<skipped>
}

if (test_and_clear_bit(HFS_FLG_ALT_MDB_DIRTY, &HFS_SB(sb)->flags) &&
HFS_SB(sb)->alt_mdb) {
<skipped>

mark_buffer_dirty(HFS_SB(sb)->alt_mdb_bh);
sync_dirty_buffer(HFS_SB(sb)->alt_mdb_bh);
}

Thanks,
Slava.

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 87320be9f0d2 Merge tag 'net-7.2-rc2' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17bdeae0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=20c9876b0f77b546
dashboard link: https://syzkaller.appspot.com/bug?extid=c149ad75e9633be0c1ad
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16c24946580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-87320be9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/754cbc66bcb5/vmlinux-87320be9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a1cc14711cba/bzImage-87320be9.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/60587e205076/mount_3.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c149ad...@syzkaller.appspotmail.com

------------[ cut here ]------------
!buffer_uptodate(bh)

WARNING: fs/buffer.c:1093 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:1093, CPU#0: syz-executor/5454
Modules linked in:
CPU: 0 UID: 0 PID: 5454 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

RIP: 0010:mark_buffer_dirty+0x299/0x410 fs/buffer.c:1093
Code: 4c 89 f7 e8 c9 11 d9 ff 49 8b 3e be 40 00 00 00 5b 41 5c 41 5e 41 5f 5d e9 d4 5e fb ff e8 9f f3 69 ff eb 8c e8 98 f3 69 ff 90 <0f> 0b 90 e9 a5 fd ff ff e8 8a f3 69 ff 90 0f 0b 90 e9 cf fd ff ff
RSP: 0018:ffffc90001c0fbf0 EFLAGS: 00010293
RAX: ffffffff825c8e78 RBX: ffff88804501cd20 RCX: ffff88803ab40000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 1ffff11006780c01 R08: ffff88804501cd27 R09: 1ffff11008a039a4
R10: dffffc0000000000 R11: ffffed1008a039a5 R12: dffffc0000000000
R13: ffff888033c06668 R14: ffff888013711c0b R15: ffff8880136da492
FS: 0000555586ef3500(0000) GS:ffff88808c54e000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f16db930000 CR3: 00000000484b1000 CR4: 0000000000352ef0
Call Trace:
<TASK>
hfs_mdb_commit+0x860/0x1160 fs/hfs/mdb.c:328
hfs_sync_fs+0x1d/0x30 fs/hfs/super.c:38
sync_filesystem+0xee/0x230 fs/sync.c:56
generic_shutdown_super+0x77/0x2d0 fs/super.c:626
kill_block_super+0x44/0x90 fs/super.c:1665
hfs_kill_super+0x41/0x50 fs/hfs/super.c:441
deactivate_locked_super+0xbc/0x130 fs/super.c:477
cleanup_mnt+0x3d3/0x460 fs/namespace.c:1317
task_work_run+0x1d9/0x270 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:70 [inline]
exit_to_user_mode_loop+0x1fa/0x730 kernel/entry/common.c:101
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
do_syscall_64+0x353/0x580 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f74cbb9f097
Code: a2 c7 05 5c 26 25 00 00 00 00 00 eb 96 e8 e1 12 00 00 90 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fff335c8fc8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007f74cbc332ca RCX: 00007f74cbb9f097
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007fff335c9080
RBP: 00007fff335c9080 R08: 00007fff335ca080 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff335ca110
R13: 00007f74cbc332ca R14: 000000000001edf7 R15: 00007fff335ca150
</TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 0e35b9b6ec0f Merge tag 'mm-hotfixes-stable-2026-07-06-17-4..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=137e7d89580000
kernel config: https://syzkaller.appspot.com/x/.config?x=20c9876b0f77b546
dashboard link: https://syzkaller.appspot.com/bug?extid=c149ad75e9633be0c1ad

compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11c55d46580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=158f6739580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-0e35b9b6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2a17ca6db8f5/vmlinux-0e35b9b6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c885024dccba/bzImage-0e35b9b6.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/6a4d05118745/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c149ad...@syzkaller.appspotmail.com

------------[ cut here ]------------
!buffer_uptodate(bh)

WARNING: fs/buffer.c:1093 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:1093, CPU#0: syz.1.1033/6784
Modules linked in:
CPU: 0 UID: 0 PID: 6784 Comm: syz.1.1033 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

RIP: 0010:mark_buffer_dirty+0x299/0x410 fs/buffer.c:1093
Code: 4c 89 f7 e8 f9 0d d9 ff 49 8b 3e be 40 00 00 00 5b 41 5c 41 5e 41 5f 5d e9 d4 5e fb ff e8 af e7 69 ff eb 8c e8 a8 e7 69 ff 90 <0f> 0b 90 e9 a5 fd ff ff e8 9a e7 69 ff 90 0f 0b 90 e9 cf fd ff ff
RSP: 0018:ffffc90005d379a8 EFLAGS: 00010293
RAX: ffffffff825c9ae8 RBX: ffff8880123aa700 RCX: ffff888034a30000

RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002

RBP: 1ffff1100a45f401 R08: ffff8880123aa707 R09: 1ffff110024754e0
R10: dffffc0000000000 R11: ffffed10024754e1 R12: dffffc0000000000
R13: ffff8880522fa668 R14: ffff888045ba945b R15: ffff888045ba9400
FS: 000055556b366500(0000) GS:ffff88808c54e000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000001b31a63fff CR3: 0000000034b1d000 CR4: 0000000000352ef0
Call Trace:
<TASK>
hfs_mdb_commit+0x503/0x1160 fs/hfs/mdb.c:309

hfs_sync_fs+0x1d/0x30 fs/hfs/super.c:38
sync_filesystem+0x1cf/0x230 fs/sync.c:66

fs_bdev_sync+0x2c/0x50 fs/super.c:1433
blkdev_flushbuf block/ioctl.c:520 [inline]
blkdev_common_ioctl+0x12e1/0x3250 block/ioctl.c:658
blkdev_ioctl+0x528/0x740 block/ioctl.c:791
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1d9239de59

Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007fffd0ece148 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f1d92625fa0 RCX: 00007f1d9239de59
RDX: 0000000000000000 RSI: 0000000000001261 RDI: 0000000000000004
RBP: 00007f1d92433e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1d92625fac R14: 00007f1d92625fa0 R15: 00007f1d92625fa0