linux-kernel - Re: [syzbot] [iomap?] kernel BUG in folio_end

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJnrk1Yo4dRVSaPCaAGkHc+in03KaTXJ+KxckhLoSrRxbEdDBg@mail.gmail.com>
Date: Tue, 4 Nov 2025 09:45:27 -0800
From: Joanne Koong <joannelkoong@...il.com>
To: syzbot <syzbot+3686758660f980b402dc@...kaller.appspotmail.com>, 
	"pmladek@...e.com" <pmladek@...e.com>, 
	"amurray@...goodpenguin.co.uk" <amurray@...goodpenguin.co.uk>
Cc: brauner@...nel.org, chao@...nel.org, djwong@...nel.org, jaegeuk@...nel.org, 
	linux-f2fs-devel@...ts.sourceforge.net, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [iomap?] kernel BUG in folio_end_read (2)

On Mon, Nov 3, 2025 at 6:43 PM syzbot
<syzbot+3686758660f980b402dc@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> WARNING in get_data
>
> loop0: detected capacity change from 0 to 16
> ------------[ cut here ]------------
> WARNING: kernel/printk/printk_ringbuffer.c:1278 at get_data+0x48a/0x840 kernel/printk/printk_ringbuffer.c:1278, CPU#1: syz.0.585/7652
> Modules linked in:
> CPU: 1 UID: 0 PID: 7652 Comm: syz.0.585 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
> RIP: 0010:get_data+0x48a/0x840 kernel/printk/printk_ringbuffer.c:1278
> Code: 83 c4 f8 48 b8 00 00 00 00 00 fc ff df 41 0f b6 04 07 84 c0 0f 85 ee 01 00 00 44 89 65 00 49 83 c5 08 eb 13 e8 a7 19 1f 00 90 <0f> 0b 90 eb 05 e8 9c 19 1f 00 45 31 ed 4c 89 e8 48 83 c4 28 5b 41
> RSP: 0018:ffffc900035170e0 EFLAGS: 00010293
> RAX: ffffffff81a1eee9 RBX: 00003fffffffffff RCX: ffff888033255b80
> RDX: 0000000000000000 RSI: 00003fffffffffff RDI: 0000000000000000
> RBP: 0000000000000012 R08: 0000000000000e55 R09: 000000325e213cc7
> R10: 000000325e213cc7 R11: 00001de4c2000037 R12: 0000000000000012
> R13: 0000000000000000 R14: ffffc90003517228 R15: 1ffffffff1bca646
> FS:  00007f44eb8da6c0(0000) GS:ffff888125fda000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f44ea9722e0 CR3: 0000000066344000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  copy_data kernel/printk/printk_ringbuffer.c:1857 [inline]
>  prb_read kernel/printk/printk_ringbuffer.c:1966 [inline]
>  _prb_read_valid+0x672/0xa90 kernel/printk/printk_ringbuffer.c:2143
>  prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2215
>  printk_get_next_message+0x15c/0x7b0 kernel/printk/printk.c:2978
>  console_emit_next_record kernel/printk/printk.c:3062 [inline]
>  console_flush_one_record kernel/printk/printk.c:3194 [inline]
>  console_flush_all+0x4cc/0xb10 kernel/printk/printk.c:3268
>  __console_flush_and_unlock kernel/printk/printk.c:3298 [inline]
>  console_unlock+0xbb/0x190 kernel/printk/printk.c:3338
>  vprintk_emit+0x4c5/0x590 kernel/printk/printk.c:2423
>  _printk+0xcf/0x120 kernel/printk/printk.c:2448
>  _erofs_printk+0x349/0x410 fs/erofs/super.c:33
>  erofs_fc_fill_super+0x1591/0x1b20 fs/erofs/super.c:746
>  get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1692
>  vfs_get_tree+0x92/0x2b0 fs/super.c:1752
>  fc_mount fs/namespace.c:1198 [inline]
>  do_new_mount_fc fs/namespace.c:3641 [inline]
>  do_new_mount+0x302/0xa10 fs/namespace.c:3717
>  do_mount fs/namespace.c:4040 [inline]
>  __do_sys_mount fs/namespace.c:4228 [inline]
>  __se_sys_mount+0x313/0x410 fs/namespace.c:4205
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f44ea99076a
> Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007f44eb8d9e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007f44eb8d9ef0 RCX: 00007f44ea99076a
> RDX: 0000200000000180 RSI: 00002000000001c0 RDI: 00007f44eb8d9eb0
> RBP: 0000200000000180 R08: 00007f44eb8d9ef0 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00002000000001c0
> R13: 00007f44eb8d9eb0 R14: 00000000000001a1 R15: 0000200000000080
>  </TASK>
>

This looks unrelated to the iomap changes and seems tied to the recent
printk console flushing changes. Hmm, maybe one of these changes
[1,2,3]?

ccing Andrew and Petr, who would know more

[1] https://lore.kernel.org/all/20251020-printk_legacy_thread_console_lock-v3-1-00f1f0ac055a@thegoodpenguin.co.uk/
[2] https://lore.kernel.org/all/20251020-printk_legacy_thread_console_lock-v3-2-00f1f0ac055a@thegoodpenguin.co.uk/
[3] https://lore.kernel.org/all/20251020-printk_legacy_thread_console_lock-v3-3-00f1f0ac055a@thegoodpenguin.co.uk/

Thanks,
Joanne

>
> Tested on:
>
> commit:         98231209 Add linux-next specific files for 20251103
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1370a292580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=43cc0e31558cb527
> dashboard link: https://syzkaller.appspot.com/bug?extid=3686758660f980b402dc
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
>
> Note: no patches were applied.