[syzbot] [usb?] general protection fault in mon_notify

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 62cc90241548 Merge tag 'mm-hotfixes-stable-2026-07-27-14-1..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=156affde580000
kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=5f4b29d9fe710a964482
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=131be449580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1467e499580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-62cc9024.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b10a9ae7e3d1/vmlinux-62cc9024.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b89124d39495/bzImage-62cc9024.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5f4b29...@syzkaller.appspotmail.com

dummy_hcd dummy_hcd.0: remove, state 4
usb usb5: USB disconnect, device number 1
dummy_hcd dummy_hcd.0: stopped
dummy_hcd dummy_hcd.0: USB bus 5 deregistered
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 UID: 0 PID: 5954 Comm: syz.0.42 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:__list_del_entry_valid_or_report+0x20/0x1d0 lib/list_debug.c:49
Code: 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 b8 00 00 00 00 00 fc ff df 41 54 55 53 48 89 fb 48 83 c7 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 5b 01 00 00 48 89 da 48 8b 6b 08 48 b8 00 00 00
RSP: 0018:ffffc9000374fa20 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: fffff520006e9f22
RDX: 0000000000000001 RSI: ffffffff8c401500 RDI: 0000000000000008
RBP: ffff88802ff87000 R08: 0000000000000000 R09: fffffbfff2244efa
R10: ffffc9000374fa40 R11: 0000000000000000 R12: 00000000fffffffe
R13: ffff88802ff870e8 R14: 0000000000000008 R15: 0000000000000000
FS: 000055556cf07500(0000) GS:ffff8880d5ddc000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc48295da08 CR3: 000000003cd5d000 CR4: 0000000000352ef0
Call Trace:
<TASK>
__list_del_entry_valid include/linux/list.h:132 [inline]
__list_del_entry include/linux/list.h:246 [inline]
list_del include/linux/list.h:260 [inline]
mon_bus_remove drivers/usb/mon/mon_main.c:203 [inline]
mon_notify+0x84/0x480 drivers/usb/mon/mon_main.c:222
notifier_call_chain+0x99/0x3f0 kernel/notifier.c:85
blocking_notifier_call_chain kernel/notifier.c:380 [inline]
blocking_notifier_call_chain+0x69/0xa0 kernel/notifier.c:368
usb_remove_hcd.cold+0x25f/0x401 drivers/usb/core/hcd.c:3084
dummy_hcd_remove+0x109/0x1e0 drivers/usb/gadget/udc/dummy_hcd.c:2761
platform_remove+0x5f/0x80 drivers/base/platform.c:1456
device_remove+0xcb/0x180 drivers/base/dd.c:616
__device_release_driver drivers/base/dd.c:1349 [inline]
device_release_driver_internal+0x44e/0x620 drivers/base/dd.c:1372
unbind_store+0xf8/0x110 drivers/base/bus.c:244
drv_attr_store+0x74/0xb0 drivers/base/bus.c:125
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc481b9de99
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:00007ffd993809e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc481e25fa0 RCX: 00007fc481b9de99
RDX: 000000000000000b RSI: 0000200000000200 RDI: 0000000000000003
RBP: 00007fc481c33eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc481e25fac R14: 00007fc481e25fa0 R15: 00007fc481e25fa0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__list_del_entry_valid_or_report+0x20/0x1d0 lib/list_debug.c:49
Code: 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 b8 00 00 00 00 00 fc ff df 41 54 55 53 48 89 fb 48 83 c7 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 5b 01 00 00 48 89 da 48 8b 6b 08 48 b8 00 00 00
RSP: 0018:ffffc9000374fa20 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: fffff520006e9f22
RDX: 0000000000000001 RSI: ffffffff8c401500 RDI: 0000000000000008
RBP: ffff88802ff87000 R08: 0000000000000000 R09: fffffbfff2244efa
R10: ffffc9000374fa40 R11: 0000000000000000 R12: 00000000fffffffe
R13: ffff88802ff870e8 R14: 0000000000000008 R15: 0000000000000000
FS: 000055556cf07500(0000) GS:ffff8880d5ddc000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc48295da08 CR3: 000000003cd5d000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
0: 90 nop
1: 90 nop
2: 90 nop
3: 90 nop
4: 90 nop
5: 90 nop
6: 90 nop
7: 90 nop
8: 90 nop
9: 90 nop
a: f3 0f 1e fa endbr64
e: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
15: fc ff df
18: 41 54 push %r12
1a: 55 push %rbp
1b: 53 push %rbx
1c: 48 89 fb mov %rdi,%rbx
1f: 48 83 c7 08 add $0x8,%rdi
23: 48 89 fa mov %rdi,%rdx
26: 48 c1 ea 03 shr $0x3,%rdx
* 2a: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction
2e: 0f 85 5b 01 00 00 jne 0x18f
34: 48 89 da mov %rbx,%rdx
37: 48 8b 6b 08 mov 0x8(%rbx),%rbp
3b: 48 rex.W
3c: b8 .byte 0xb8
3d: 00 00 add %al,(%rax)


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