linux-kernel - Re: [syzbot] [comedi?] memory leak in do_cmd

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Message-ID: <693fc12e.a70a0220.104cf0.0338.GAE@google.com>
Date: Mon, 15 Dec 2025 00:05:02 -0800
From: syzbot <syzbot+f238baf6ded841b5a82e@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	xiaopei01@...inos.cn, xiaopeitux@...mail.com
Subject: Re: [syzbot] [comedi?] memory leak in do_cmd_ioctl

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel paging request in do_cmd_ioctl

BUG: unable to handle page fault for address: ffffec5e00000008
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0 
Oops: Oops: 0000 [#1] SMP PTI
CPU: 1 UID: 0 PID: 6735 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:page_slab mm/slab.h:142 [inline]
RIP: 0010:kfree+0x6c/0x3d0 mm/slub.c:6869
Code: 80 48 01 df 0f 82 6a 03 00 00 48 c7 c0 00 00 00 80 48 2b 05 66 9b 14 05 48 01 c7 48 c1 ef 0c 48 c1 e7 06 48 03 3d 44 9b 14 05 <48> 8b 47 08 a8 01 4c 8d 60 ff 4c 0f 44 e7 41 80 7c 24 33 f5 0f 85
RSP: 0018:ffffc9000217fd50 EFLAGS: 00010286
RAX: 0000777f80000000 RBX: 00002000000000c0 RCX: ffffffff844b815c
RDX: ffff8881244d9180 RSI: ffffffff844ab69a RDI: ffffec5e00000000
RBP: ffffc9000217fda0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000010 R11: ffffffff81000130 R12: ffff8881136bc198
R13: ffff8881458db700 R14: ffff8881458db500 R15: ffffc9000217fe28
FS:  00007feb67bfe6c0(0000) GS:ffff8881b266b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffec5e00000008 CR3: 000000010a316000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 do_cmd_ioctl.part.0+0x18a/0x360 drivers/comedi/comedi_fops.c:1896
 do_cmd_ioctl drivers/comedi/comedi_fops.c:1858 [inline]
 comedi_unlocked_ioctl+0xdea/0x1300 drivers/comedi/comedi_fops.c:2321
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0xf4/0x140 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7feb6858f749
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:00007feb67bfe038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007feb687e5fa0 RCX: 00007feb6858f749
RDX: 0000200000000180 RSI: 0000000080506409 RDI: 0000000000000003
RBP: 00007feb68613f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007feb687e6038 R14: 00007feb687e5fa0 R15: 00007fff6cee0be8
 </TASK>
Modules linked in:
CR2: ffffec5e00000008
---[ end trace 0000000000000000 ]---
RIP: 0010:page_slab mm/slab.h:142 [inline]
RIP: 0010:kfree+0x6c/0x3d0 mm/slub.c:6869
Code: 80 48 01 df 0f 82 6a 03 00 00 48 c7 c0 00 00 00 80 48 2b 05 66 9b 14 05 48 01 c7 48 c1 ef 0c 48 c1 e7 06 48 03 3d 44 9b 14 05 <48> 8b 47 08 a8 01 4c 8d 60 ff 4c 0f 44 e7 41 80 7c 24 33 f5 0f 85
RSP: 0018:ffffc9000217fd50 EFLAGS: 00010286
RAX: 0000777f80000000 RBX: 00002000000000c0 RCX: ffffffff844b815c
RDX: ffff8881244d9180 RSI: ffffffff844ab69a RDI: ffffec5e00000000
RBP: ffffc9000217fda0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000010 R11: ffffffff81000130 R12: ffff8881136bc198
R13: ffff8881458db700 R14: ffff8881458db500 R15: ffffc9000217fe28
FS:  00007feb67bfe6c0(0000) GS:ffff8881b266b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffec5e00000008 CR3: 000000010a316000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	80 48 01 df          	orb    $0xdf,0x1(%rax)
   4:	0f 82 6a 03 00 00    	jb     0x374
   a:	48 c7 c0 00 00 00 80 	mov    $0xffffffff80000000,%rax
  11:	48 2b 05 66 9b 14 05 	sub    0x5149b66(%rip),%rax        # 0x5149b7e
  18:	48 01 c7             	add    %rax,%rdi
  1b:	48 c1 ef 0c          	shr    $0xc,%rdi
  1f:	48 c1 e7 06          	shl    $0x6,%rdi
  23:	48 03 3d 44 9b 14 05 	add    0x5149b44(%rip),%rdi        # 0x5149b6e
* 2a:	48 8b 47 08          	mov    0x8(%rdi),%rax <-- trapping instruction
  2e:	a8 01                	test   $0x1,%al
  30:	4c 8d 60 ff          	lea    -0x1(%rax),%r12
  34:	4c 0f 44 e7          	cmove  %rdi,%r12
  38:	41 80 7c 24 33 f5    	cmpb   $0xf5,0x33(%r12)
  3e:	0f                   	.byte 0xf
  3f:	85                   	.byte 0x85


Tested on:

commit:         8f0b4cce Linux 6.19-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16bd411a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d60836e327fd6756
dashboard link: https://syzkaller.appspot.com/bug?extid=f238baf6ded841b5a82e
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=166d411a580000