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

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=135b16b9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=ccaeedf06fe422068ae0
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/824c8ce85a0f/disk-62cc9024.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a1e6cc0e8f11/vmlinux-62cc9024.xz
kernel image: https://storage.googleapis.com/syzbot-assets/807679f73b90/bzImage-62cc9024.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

Oops: general protection fault, probably for non-canonical address 0xdffffc000000000c: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000060-0x0000000000000067]
CPU: 1 UID: 0 PID: 22936 Comm: kworker/1:2H Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: events_highpri f_midi_in_work
RIP: 0010:dummy_queue+0x1ba/0xb00 drivers/usb/gadget/udc/dummy_hcd.c:737
Code: 00 49 83 bc 24 c8 05 00 00 00 0f 84 a6 07 00 00 e8 6b 30 39 fa 49 8d 7f 60 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 4f 07 00 00 45 8b 7f 60 31 ff
RSP: 0018:ffffc9000784fa28 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: ffff888045374710 RCX: ffffffff87d12f5f
RDX: 000000000000000c RSI: ffffffff87d12fd5 RDI: 0000000000000060
RBP: ffff88802b1640e0 R08: 0000000000000005 R09: 0000000000000005
R10: 0000000000000003 R11: 0000000000000000 R12: ffff88802b164c00
R13: ffff888045374700 R14: ffff88802b1640d8 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888123edc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b322fdff8 CR3: 0000000029d76000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 usb_ep_queue+0xfa/0x3c0 drivers/usb/gadget/udc/core.c:305
 f_midi_do_transmit drivers/usb/gadget/function/f_midi.c:659 [inline]
 f_midi_transmit drivers/usb/gadget/function/f_midi.c:687 [inline]
 f_midi_in_work+0x9b0/0x1580 drivers/usb/gadget/function/f_midi.c:707
 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
 process_scheduled_works kernel/workqueue.c:3405 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:dummy_queue+0x1ba/0xb00 drivers/usb/gadget/udc/dummy_hcd.c:737
Code: 00 49 83 bc 24 c8 05 00 00 00 0f 84 a6 07 00 00 e8 6b 30 39 fa 49 8d 7f 60 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 4f 07 00 00 45 8b 7f 60 31 ff
RSP: 0018:ffffc9000784fa28 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: ffff888045374710 RCX: ffffffff87d12f5f
RDX: 000000000000000c RSI: ffffffff87d12fd5 RDI: 0000000000000060
RBP: ffff88802b1640e0 R08: 0000000000000005 R09: 0000000000000005
R10: 0000000000000003 R11: 0000000000000000 R12: ffff88802b164c00
R13: ffff888045374700 R14: ffff88802b1640d8 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888123edc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b322fdff8 CR3: 0000000029d76000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	00 49 83             	add    %cl,-0x7d(%rcx)
   3:	bc 24 c8 05 00       	mov    $0x5c824,%esp
   8:	00 00                	add    %al,(%rax)
   a:	0f 84 a6 07 00 00    	je     0x7b6
  10:	e8 6b 30 39 fa       	call   0xfa393080
  15:	49 8d 7f 60          	lea    0x60(%r15),%rdi
  19:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  20:	fc ff df
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	0f b6 04 02          	movzbl (%rdx,%rax,1),%eax <-- trapping instruction
  2e:	84 c0                	test   %al,%al
  30:	74 08                	je     0x3a
  32:	3c 03                	cmp    $0x3,%al
  34:	0f 8e 4f 07 00 00    	jle    0x789
  3a:	45 8b 7f 60          	mov    0x60(%r15),%r15d
  3e:	31 ff                	xor    %edi,%edi


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