linux-kernel - [syzbot] [comedi?] possible deadlock in comedi_do

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>] [day] [month] [year] [list]
Message-ID: <68e37b51.050a0220.2c17c1.0042.GAE@google.com>
Date: Mon, 06 Oct 2025 01:18:25 -0700
From: syzbot <syzbot+4a6138c17a47937dcea1@...kaller.appspotmail.com>
To: abbotti@....co.uk, hsweeten@...ionengravers.com, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [comedi?] possible deadlock in comedi_do_insn

Hello,

syzbot found the following issue on:

HEAD commit:    3b9b1f8df454 Add linux-next specific files for 20250929
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10e08458580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3c7c078c891391b1
dashboard link: https://syzkaller.appspot.com/bug?extid=4a6138c17a47937dcea1
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1ccfc1a8eb22/disk-3b9b1f8d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c4e52fa84079/vmlinux-3b9b1f8d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9eacf34feeec/bzImage-3b9b1f8d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4a6138c17a47937dcea1@...kaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.3.705/8631 is trying to acquire lock:
ffff88814c4ae0f8 (&dev->mutex#4){+.+.}-{4:4}, at: comedi_do_insn+0x38/0x3d0 drivers/comedi/kcomedilib/kcomedilib_main.c:73

but task is already holding lock:
ffff88814c4ac8f8 (&dev->mutex#4){+.+.}-{4:4}, at: comedi_unlocked_ioctl+0x13a/0x1020 drivers/comedi/comedi_fops.c:2166

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev->mutex#4);
  lock(&dev->mutex#4);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz.3.705/8631:
 #0: ffff88814c4ac8f8 (&dev->mutex#4){+.+.}-{4:4}, at: comedi_unlocked_ioctl+0x13a/0x1020 drivers/comedi/comedi_fops.c:2166

stack backtrace:
CPU: 0 UID: 0 PID: 8631 Comm: syz.3.705 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
 comedi_do_insn+0x38/0x3d0 drivers/comedi/kcomedilib/kcomedilib_main.c:73
 comedi_dio_bitfield2+0x2d7/0x3b0 drivers/comedi/kcomedilib/kcomedilib_main.c:204
 bonding_dio_insn_bits+0x2a5/0x590 drivers/comedi/drivers/comedi_bond.c:100
 insn_rw_emulate_bits+0x34d/0x5f0 drivers/comedi/drivers.c:642
 parse_insn+0xa26/0x1910 drivers/comedi/comedi_fops.c:1454
 do_insnlist_ioctl+0x331/0x690 drivers/comedi/comedi_fops.c:1594
 comedi_unlocked_ioctl+0xdeb/0x1020 drivers/comedi/comedi_fops.c:2298
 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+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f96e618eec9
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:00007f96e700b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f96e63e5fa0 RCX: 00007f96e618eec9
RDX: 0000200000000080 RSI: 000000008010640b RDI: 0000000000000003
RBP: 00007f96e6211f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f96e63e6038 R14: 00007f96e63e5fa0 R15: 00007ffde94ae9d8
 </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 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