[syzbot] [sound?] [usb?] general protection fault in snd_usbmidi_do_output

[syzbot <syzbot+f02665daa2abeef4a947@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    3b08f56fbbb9 Merge tag 'x86-urgent-2025-09-20' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=176950e2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=927198eca77e75d9
dashboard link: https://syzkaller.appspot.com/bug?extid=f02665daa2abeef4a947
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14006712580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14e950e2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/459cbf9146bd/disk-3b08f56f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6836a598801b/vmlinux-3b08f56f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/92e1bc34a72e/bzImage-3b08f56f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f02665daa2abeef4a947@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000011: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000088-0x000000000000008f]
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:snd_usbmidi_do_output+0x22d/0x570 sound/usb/midi.c:310
Code: f8 48 c1 e8 03 42 80 3c 28 00 0f 85 14 03 00 00 89 d8 48 c1 e0 04 4c 8b 64 05 08 49 8d 84 24 88 00 00 00 48 89 c2 48 c1 ea 03 <42> 0f b6 14 2a 84 d2 74 09 80 fa 03 0f 8e ad 02 00 00 48 8b 74 24
RSP: 0018:ffffc90000007b80 EFLAGS: 00010016
RAX: 0000000000000088 RBX: 0000000000000000 RCX: ffffffff894338b8
RDX: 0000000000000011 RSI: ffffffff894338c6 RDI: ffff88805e0fc008
RBP: ffff88805e0fc000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffffed100bc1f80f R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8881246b3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32d63fff CR3: 000000007e1d5000 CR4: 0000000000350ef0
Call Trace:
 <IRQ>
 snd_usbmidi_error_timer+0x119/0x410 sound/usb/midi.c:362
 call_timer_fn+0x19a/0x620 kernel/time/timer.c:1747
 expire_timers kernel/time/timer.c:1798 [inline]
 __run_timers+0x6ef/0x960 kernel/time/timer.c:2372
 __run_timer_base kernel/time/timer.c:2384 [inline]
 __run_timer_base kernel/time/timer.c:2376 [inline]
 run_timer_base+0x114/0x190 kernel/time/timer.c:2393
 run_timer_softirq+0x1a/0x40 kernel/time/timer.c:2403
 handle_softirqs+0x219/0x8e0 kernel/softirq.c:579
 __do_softirq kernel/softirq.c:613 [inline]
 invoke_softirq kernel/softirq.c:453 [inline]
 __irq_exit_rcu+0x109/0x170 kernel/softirq.c:680
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1050
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:82
Code: 1d 63 02 e9 9e 5a 7d f5 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d d3 16 17 00 fb f4 <e9> 77 5a 7d f5 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffffff8e207e08 EFLAGS: 000002c2
RAX: 00000000000ab2b9 RBX: 0000000000000000 RCX: ffffffff8b92fb49
RDX: 0000000000000000 RSI: ffffffff8de5156d RDI: ffffffff8c163a00
RBP: fffffbfff1c52ef8 R08: 0000000000000001 R09: ffffed1017086655
R10: ffff8880b84332ab R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff8e2977c0 R14: ffffffff90abad90 R15: 0000000000000000
 arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:757
 default_idle_call+0x6d/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:190 [inline]
 do_idle+0x391/0x510 kernel/sched/idle.c:330
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:428
 rest_init+0x16b/0x2b0 init/main.c:744
 start_kernel+0x3ee/0x4d0 init/main.c:1097
 x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:307
 x86_64_start_kernel+0x130/0x190 arch/x86/kernel/head64.c:288
 common_startup_64+0x13e/0x148
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:snd_usbmidi_do_output+0x22d/0x570 sound/usb/midi.c:310
Code: f8 48 c1 e8 03 42 80 3c 28 00 0f 85 14 03 00 00 89 d8 48 c1 e0 04 4c 8b 64 05 08 49 8d 84 24 88 00 00 00 48 89 c2 48 c1 ea 03 <42> 0f b6 14 2a 84 d2 74 09 80 fa 03 0f 8e ad 02 00 00 48 8b 74 24
RSP: 0018:ffffc90000007b80 EFLAGS: 00010016
RAX: 0000000000000088 RBX: 0000000000000000 RCX: ffffffff894338b8
RDX: 0000000000000011 RSI: ffffffff894338c6 RDI: ffff88805e0fc008
RBP: ffff88805e0fc000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffffed100bc1f80f R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8881246b3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32d63fff CR3: 000000007e1d5000 CR4: 0000000000350ef0
----------------
Code disassembly (best guess):
   0:	f8                   	clc
   1:	48 c1 e8 03          	shr    $0x3,%rax
   5:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
   a:	0f 85 14 03 00 00    	jne    0x324
  10:	89 d8                	mov    %ebx,%eax
  12:	48 c1 e0 04          	shl    $0x4,%rax
  16:	4c 8b 64 05 08       	mov    0x8(%rbp,%rax,1),%r12
  1b:	49 8d 84 24 88 00 00 	lea    0x88(%r12),%rax
  22:	00
  23:	48 89 c2             	mov    %rax,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	42 0f b6 14 2a       	movzbl (%rdx,%r13,1),%edx <-- trapping instruction
  2f:	84 d2                	test   %dl,%dl
  31:	74 09                	je     0x3c
  33:	80 fa 03             	cmp    $0x3,%dl
  36:	0f 8e ad 02 00 00    	jle    0x2e9
  3c:	48                   	rex.W
  3d:	8b                   	.byte 0x8b
  3e:	74 24                	je     0x64


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