linux-kernel - Re: [syzbot] [comedi?] BUG: unable to handle kernel paging request in dt2815

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Message-ID: <697703d4.050a0220.1d05e9.000e.GAE@google.com>
Date: Sun, 25 Jan 2026 22:04:04 -0800
From: syzbot <syzbot+72f94b474d6e50b71ffc@...kaller.appspotmail.com>
To: kartikey406@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [comedi?] BUG: unable to handle kernel paging request in dt2815_attach

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel NULL pointer dereference in dt2815_attach

BUG: kernel NULL pointer dereference, address: 0000000000000390
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 365dc067 P4D 365dc067 PUD 0 
Oops: Oops: 0002 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5841 Comm: syz.0.18 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:__outb arch/x86/include/asm/shared/io.h:22 [inline]
RIP: 0010:dt2815_attach+0x4f3/0xa40 drivers/comedi/drivers/dt2815.c:179
Code: 24 4c 8d b8 d0 01 00 00 4c 89 fb 48 c1 eb 03 42 80 3c 2b 00 74 08 4c 89 ff e8 a9 00 4c f9 48 8b 04 24 8b 90 d0 01 00 00 ff c2 <31> 66 90 bf e8 03 00 00 be b8 0b 00 00 ba 02 00 00 00 e8 56 0a 9e
RSP: 0018:ffffc90002befa88 EFLAGS: 00010206
RAX: ffff888040c87000 RBX: 1ffff11008190e3a RCX: 0000000000000000
RDX: 000000000000007e RSI: 0000000000000400 RDI: 0000000000000000
RBP: 0000000000000400 R08: 0000000000000dc0 R09: 00000000ffffffff
R10: 000000000000000a R11: ffffffff81ae5bd0 R12: ffffc90002befc04
R13: dffffc0000000000 R14: ffffc90002befbc0 R15: ffff888040c871d0
FS:  00007fa9eb7d96c0(0000) GS:ffff88808cf1b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000390 CR3: 00000000595eb000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 comedi_device_attach+0x51f/0x720 drivers/comedi/drivers.c:1069
 do_devconfig_ioctl drivers/comedi/comedi_fops.c:928 [inline]
 comedi_unlocked_ioctl+0x701/0x1240 drivers/comedi/comedi_fops.c:2240
 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+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa9ea99acb9
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:00007fa9eb7d9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa9eac15fa0 RCX: 00007fa9ea99acb9
RDX: 0000200000000080 RSI: 0000000040946400 RDI: 0000000000000003
RBP: 00007fa9eaa08bf7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa9eac16038 R14: 00007fa9eac15fa0 R15: 00007fff0dbc24e8
 </TASK>
Modules linked in:
CR2: 0000000000000390
---[ end trace 0000000000000000 ]---
RIP: 0010:__outb arch/x86/include/asm/shared/io.h:22 [inline]
RIP: 0010:dt2815_attach+0x4f3/0xa40 drivers/comedi/drivers/dt2815.c:179
Code: 24 4c 8d b8 d0 01 00 00 4c 89 fb 48 c1 eb 03 42 80 3c 2b 00 74 08 4c 89 ff e8 a9 00 4c f9 48 8b 04 24 8b 90 d0 01 00 00 ff c2 <31> 66 90 bf e8 03 00 00 be b8 0b 00 00 ba 02 00 00 00 e8 56 0a 9e
RSP: 0018:ffffc90002befa88 EFLAGS: 00010206
RAX: ffff888040c87000 RBX: 1ffff11008190e3a RCX: 0000000000000000
RDX: 000000000000007e RSI: 0000000000000400 RDI: 0000000000000000
RBP: 0000000000000400 R08: 0000000000000dc0 R09: 00000000ffffffff
R10: 000000000000000a R11: ffffffff81ae5bd0 R12: ffffc90002befc04
R13: dffffc0000000000 R14: ffffc90002befbc0 R15: ffff888040c871d0
FS:  00007fa9eb7d96c0(0000) GS:ffff88808cf1b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000390 CR3: 00000000595eb000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	24 4c                	and    $0x4c,%al
   2:	8d b8 d0 01 00 00    	lea    0x1d0(%rax),%edi
   8:	4c 89 fb             	mov    %r15,%rbx
   b:	48 c1 eb 03          	shr    $0x3,%rbx
   f:	42 80 3c 2b 00       	cmpb   $0x0,(%rbx,%r13,1)
  14:	74 08                	je     0x1e
  16:	4c 89 ff             	mov    %r15,%rdi
  19:	e8 a9 00 4c f9       	call   0xf94c00c7
  1e:	48 8b 04 24          	mov    (%rsp),%rax
  22:	8b 90 d0 01 00 00    	mov    0x1d0(%rax),%edx
  28:	ff c2                	inc    %edx
* 2a:	31 66 90             	xor    %esp,-0x70(%rsi) <-- trapping instruction
  2d:	bf e8 03 00 00       	mov    $0x3e8,%edi
  32:	be b8 0b 00 00       	mov    $0xbb8,%esi
  37:	ba 02 00 00 00       	mov    $0x2,%edx
  3c:	e8                   	.byte 0xe8
  3d:	56                   	push   %rsi
  3e:	0a                   	.byte 0xa
  3f:	9e                   	sahf


Tested on:

commit:         63804fed Linux 6.19-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1083f294580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e2e5d7c9c1e01cf4
dashboard link: https://syzkaller.appspot.com/bug?extid=72f94b474d6e50b71ffc
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=164bfe8a580000