Message-ID: <aiji665th2iqsrwedypd2zw3guzykottzooslqja66tj4aqcr3@2hpzlh6ut4xp>
Date: Thu, 2 Oct 2025 10:07:58 +0200
From: Jan Kara <jack@...e.cz>
To: syzbot <syzbot+47680984f2d4969027ea@...kaller.appspotmail.com>
Cc: brauner@...nel.org, chao@...nel.org, dan.j.williams@...el.com, 
	jack@...e.cz, linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, syzkaller-bugs@...glegroups.com, 
	viro@...iv.linux.org.uk, willy@...radead.org, xiang@...nel.org
Subject: Re: [syzbot] [erofs?] WARNING in dax_iomap_rw

Hello,

On Wed 01-10-25 17:10:33, syzbot wrote:
> syzbot found the following issue on:
> 
> HEAD commit:    50c19e20ed2e Merge tag 'nolibc-20250928-for-6.18-1' of git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=136ee6e2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ee1d7eda39c03d2c
> dashboard link: https://syzkaller.appspot.com/bug?extid=47680984f2d4969027ea
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1181036f980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15875d04580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-50c19e20.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/33a22a854fe0/vmlinux-50c19e20.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/e68f79994eb8/bzImage-50c19e20.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/71839d8fa466/mount_0.gz
>   fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=17630a7c580000)
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+47680984f2d4969027ea@...kaller.appspotmail.com
> 
> loop0: detected capacity change from 0 to 16
> erofs (device loop0): mounted with root inode @ nid 36.
> process 'syz.0.17' launched './file2' with NULL argv: empty string added
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5507 at fs/dax.c:1756 dax_iomap_rw+0xe34/0xed0 fs/dax.c:1756
> Modules linked in:

OK, this is a bit overzealous assert in dax_iomap_rw() which triggers for
erofs. I'll send a fix.

								Honza

> CPU: 0 UID: 0 PID: 5507 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:dax_iomap_rw+0xe34/0xed0 fs/dax.c:1756
> Code: ff ff 49 bd 00 00 00 00 00 fc ff df eb 84 e8 33 d7 6f ff 90 0f 0b 90 80 8c 24 c4 01 00 00 01 e9 b9 f4 ff ff e8 1d d7 6f ff 90 <0f> 0b 90 e9 ab f4 ff ff 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c 56 f3
> RSP: 0018:ffffc9000296f840 EFLAGS: 00010293
> RAX: ffffffff824eae63 RBX: ffffc9000296fc00 RCX: ffff88801f938000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: ffffc9000296fb30 R08: ffffc9000296fa9f R09: 0000000000000000
> R10: ffffc9000296f9f8 R11: fffff5200052df54 R12: 1ffff9200052df80
> R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000001
> FS:  0000555575829500(0000) GS:ffff88808d967000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f41f4179286 CR3: 0000000050011000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  __kernel_read+0x4cc/0x960 fs/read_write.c:530
>  prepare_binprm fs/exec.c:1609 [inline]
>  search_binary_handler fs/exec.c:1656 [inline]
>  exec_binprm fs/exec.c:1702 [inline]
>  bprm_execve+0x8ce/0x1450 fs/exec.c:1754
>  do_execveat_common+0x510/0x6a0 fs/exec.c:1860
>  do_execveat fs/exec.c:1945 [inline]
>  __do_sys_execveat fs/exec.c:2019 [inline]
>  __se_sys_execveat fs/exec.c:2013 [inline]
>  __x64_sys_execveat+0xc4/0xe0 fs/exec.c:2013
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f7556f8eec9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffea3815728 EFLAGS: 00000246 ORIG_RAX: 0000000000000142
> RAX: ffffffffffffffda RBX: 00007f75571e5fa0 RCX: 00007f7556f8eec9
> RDX: 0000000000000000 RSI: 0000200000000000 RDI: ffffffffffffff9c
> RBP: 00007f7557011f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f75571e5fa0 R14: 00007f75571e5fa0 R15: 0000000000000005
>  </TASK>
> 
> 
> ---
> 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@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> 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.
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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