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

[syzbot]

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+f02665...@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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#syz test: git://repo/address.git branch-or-commit-hash
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#syz undup

[Hillf Danton]

> Date: Mon, 22 Sep 2025 09:54:28 -0700 [thread overview]

> 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

#syz test upstream master

--- x/sound/usb/midi.c
+++ y/sound/usb/midi.c
@@ -307,6 +307,8 @@ static void snd_usbmidi_do_output(struct
for (;;) {
if (!(ep->active_urbs & (1 << urb_index))) {
urb = ep->urbs[urb_index].urb;
+ if (!urb)
+ goto next;
urb->transfer_buffer_length = 0;
ep->umidi->usb_protocol_ops->output(ep, urb);
if (urb->transfer_buffer_length == 0)
@@ -319,6 +321,7 @@ static void snd_usbmidi_do_output(struct
break;
ep->active_urbs |= 1 << urb_index;
}
+ next:
if (++urb_index >= OUTPUT_URBS)
urb_index = 0;
if (urb_index == ep->next_urb)
@@ -1396,13 +1399,19 @@ static int snd_usbmidi_in_endpoint_creat
static void snd_usbmidi_out_endpoint_clear(struct snd_usb_midi_out_endpoint *ep)
{
unsigned int i;
+ unsigned long flags;

+ spin_lock_irqsave(&ep->buffer_lock, flags);
for (i = 0; i < OUTPUT_URBS; ++i)
if (ep->urbs[i].urb) {
- free_urb_and_buffer(ep->umidi, ep->urbs[i].urb,
- ep->max_transfer);
+ struct urb *urb = ep->urbs[i].urb;
+
ep->urbs[i].urb = NULL;
+ spin_unlock_irqrestore(&ep->buffer_lock, flags);
+ free_urb_and_buffer(ep->umidi, urb, ep->max_transfer);
+ spin_lock_irqsave(&ep->buffer_lock, flags);
}
+ spin_unlock_irqrestore(&ep->buffer_lock, flags);
}

static void snd_usbmidi_out_endpoint_delete(struct snd_usb_midi_out_endpoint *ep)
--

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Write in snd_usbmidi_in_urb_complete

==================================================================
BUG: KASAN: slab-use-after-free in snd_usbmidi_in_urb_complete+0x389/0x3c0 sound/usb/midi.c:251
Write of size 1 at addr ffff88805cb67943 by task kworker/u8:7/1159

CPU: 1 UID: 0 PID: 1159 Comm: kworker/u8:7 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025

Workqueue: netns cleanup_net
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xcd/0x630 mm/kasan/report.c:482
kasan_report+0xe0/0x110 mm/kasan/report.c:595
snd_usbmidi_in_urb_complete+0x389/0x3c0 sound/usb/midi.c:251
__usb_hcd_giveback_urb+0x38b/0x610 drivers/usb/core/hcd.c:1661
usb_hcd_giveback_urb+0x39b/0x450 drivers/usb/core/hcd.c:1745
dummy_timer+0x1814/0x3a30 drivers/usb/gadget/udc/dummy_hcd.c:1995
__run_hrtimer kernel/time/hrtimer.c:1761 [inline]
__hrtimer_run_queues+0x202/0xad0 kernel/time/hrtimer.c:1825
hrtimer_run_softirq+0x17d/0x350 kernel/time/hrtimer.c:1842

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:console_flush_all+0x9a2/0xc60 kernel/printk/printk.c:3227
Code: 00 e8 b2 d3 28 00 9c 5b 81 e3 00 02 00 00 31 ff 48 89 de e8 30 e8 20 00 48 85 db 0f 85 55 01 00 00 e8 b2 ec 20 00 fb 4c 89 e0 <48> c1 e8 03 42 80 3c 38 00 0f 84 11 ff ff ff 4c 89 e7 e8 67 5f 86
RSP: 0018:ffffc900038ff550 EFLAGS: 00000293
RAX: ffffffff8f2f1698 RBX: 0000000000000000 RCX: ffffffff819ab010
RDX: ffff888028051e00 RSI: ffffffff819ab01e RDI: 0000000000000007
RBP: 0000000000000001 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 615f6e616d746162 R12: ffffffff8f2f1698
R13: ffffffff8f2f1640 R14: ffffc900038ff5e0 R15: dffffc0000000000
__console_flush_and_unlock kernel/printk/printk.c:3285 [inline]
console_unlock+0xd8/0x210 kernel/printk/printk.c:3325
vprintk_emit+0x418/0x6d0 kernel/printk/printk.c:2450
_printk+0xc7/0x100 kernel/printk/printk.c:2475
batadv_hardif_disable_interface+0x2b2/0xe70 net/batman-adv/hard-interface.c:826
batadv_meshif_destroy_netlink+0x79/0x150 net/batman-adv/mesh-interface.c:1106
default_device_exit_batch+0x769/0xaf0 net/core/dev.c:12728
ops_exit_list net/core/net_namespace.c:204 [inline]
ops_undo_list+0x363/0xab0 net/core/net_namespace.c:251
cleanup_net+0x408/0x890 net/core/net_namespace.c:682
process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
kthread+0x3c5/0x780 kernel/kthread.c:463
ret_from_fork+0x56d/0x730 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 6562:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
kasan_save_track+0x14/0x30 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:405
kmalloc_noprof include/linux/slab.h:905 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
snd_usbmidi_in_endpoint_create+0x8c/0xa70 sound/usb/midi.c:1345
snd_usbmidi_create_endpoints_midiman+0x4c4/0xaf0 sound/usb/midi.c:2372
__snd_usbmidi_create+0x14a4/0x1e90 sound/usb/midi.c:2655
snd_usb_midi_v2_create+0x1ad/0x42d0 sound/usb/midi2.c:1178
snd_usb_create_quirk+0xad/0x140 sound/usb/quirks.c:541
usb_audio_probe+0x7f7/0x3cf0 sound/usb/card.c:976
usb_probe_interface+0x303/0xa40 drivers/usb/core/driver.c:396
call_driver_probe drivers/base/dd.c:581 [inline]
really_probe+0x241/0xa90 drivers/base/dd.c:659
__driver_probe_device+0x1de/0x440 drivers/base/dd.c:801
driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:831
__device_attach_driver+0x1df/0x310 drivers/base/dd.c:959
bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:462
__device_attach+0x1e4/0x4b0 drivers/base/dd.c:1031
bus_probe_device+0x17f/0x1c0 drivers/base/bus.c:537
device_add+0x1148/0x1aa0 drivers/base/core.c:3689
usb_set_configuration+0x1187/0x1e20 drivers/usb/core/message.c:2210
usb_generic_driver_probe+0xb1/0x110 drivers/usb/core/generic.c:250
usb_probe_device+0xef/0x3e0 drivers/usb/core/driver.c:291
call_driver_probe drivers/base/dd.c:581 [inline]
really_probe+0x241/0xa90 drivers/base/dd.c:659
__driver_probe_device+0x1de/0x440 drivers/base/dd.c:801
driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:831
__device_attach_driver+0x1df/0x310 drivers/base/dd.c:959
bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:462
__device_attach+0x1e4/0x4b0 drivers/base/dd.c:1031
bus_probe_device+0x17f/0x1c0 drivers/base/bus.c:537
device_add+0x1148/0x1aa0 drivers/base/core.c:3689
usb_new_device+0xd07/0x1a60 drivers/usb/core/hub.c:2694
hub_port_connect drivers/usb/core/hub.c:5566 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5706 [inline]
port_event drivers/usb/core/hub.c:5870 [inline]
hub_event+0x2f34/0x4fe0 drivers/usb/core/hub.c:5952
process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
kthread+0x3c5/0x780 kernel/kthread.c:463
ret_from_fork+0x56d/0x730 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 6562:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
kasan_save_track+0x14/0x30 mm/kasan/common.c:68
kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:243 [inline]
__kasan_slab_free+0x60/0x70 mm/kasan/common.c:275
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2422 [inline]
slab_free mm/slub.c:4695 [inline]
kfree+0x2b4/0x4d0 mm/slub.c:4894
snd_usbmidi_free sound/usb/midi.c:1539 [inline]
snd_usbmidi_rawmidi_free+0xb3/0x130 sound/usb/midi.c:1600
snd_rawmidi_free.part.0+0x398/0x560 sound/core/rawmidi.c:1934
snd_rawmidi_free sound/core/rawmidi.c:1923 [inline]
snd_rawmidi_dev_free+0x3e/0x60 sound/core/rawmidi.c:1945
__snd_device_free+0x1a7/0x410 sound/core/device.c:76
snd_device_free_all+0xf3/0x220 sound/core/device.c:233
snd_card_do_free sound/core/init.c:587 [inline]
release_card_device+0x77/0x1d0 sound/core/init.c:153
device_release+0xa4/0x240 drivers/base/core.c:2565
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x1e7/0x5a0 lib/kobject.c:737
put_device+0x1f/0x30 drivers/base/core.c:3797
snd_card_free_when_closed sound/core/init.c:618 [inline]
snd_card_free_when_closed sound/core/init.c:612 [inline]
snd_card_free+0x11a/0x190 sound/core/init.c:650
usb_audio_probe+0x1507/0x3cf0 sound/usb/card.c:1034
usb_probe_interface+0x303/0xa40 drivers/usb/core/driver.c:396
call_driver_probe drivers/base/dd.c:581 [inline]
really_probe+0x241/0xa90 drivers/base/dd.c:659
__driver_probe_device+0x1de/0x440 drivers/base/dd.c:801
driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:831
__device_attach_driver+0x1df/0x310 drivers/base/dd.c:959
bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:462
__device_attach+0x1e4/0x4b0 drivers/base/dd.c:1031
bus_probe_device+0x17f/0x1c0 drivers/base/bus.c:537
device_add+0x1148/0x1aa0 drivers/base/core.c:3689
usb_set_configuration+0x1187/0x1e20 drivers/usb/core/message.c:2210
usb_generic_driver_probe+0xb1/0x110 drivers/usb/core/generic.c:250
usb_probe_device+0xef/0x3e0 drivers/usb/core/driver.c:291
call_driver_probe drivers/base/dd.c:581 [inline]
really_probe+0x241/0xa90 drivers/base/dd.c:659
__driver_probe_device+0x1de/0x440 drivers/base/dd.c:801
driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:831
__device_attach_driver+0x1df/0x310 drivers/base/dd.c:959
bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:462
__device_attach+0x1e4/0x4b0 drivers/base/dd.c:1031
bus_probe_device+0x17f/0x1c0 drivers/base/bus.c:537
device_add+0x1148/0x1aa0 drivers/base/core.c:3689
usb_new_device+0xd07/0x1a60 drivers/usb/core/hub.c:2694
hub_port_connect drivers/usb/core/hub.c:5566 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5706 [inline]
port_event drivers/usb/core/hub.c:5870 [inline]
hub_event+0x2f34/0x4fe0 drivers/usb/core/hub.c:5952
process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
kthread+0x3c5/0x780 kernel/kthread.c:463
ret_from_fork+0x56d/0x730 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff88805cb67800
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 323 bytes inside of
freed 512-byte region [ffff88805cb67800, ffff88805cb67a00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88805cb65400 pfn:0x5cb64
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000240 ffff88801b841c80 ffffea0001cc1910 ffffea0000c27910
raw: ffff88805cb65400 000000000010000a 00000000f5000000 0000000000000000
head: 00fff00000000240 ffff88801b841c80 ffffea0001cc1910 ffffea0000c27910
head: ffff88805cb65400 000000000010000a 00000000f5000000 0000000000000000
head: 00fff00000000002 ffffea000172d901 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6539, tgid 6539 (kworker/1:8), ts 490477154046, free_ts 189435416717
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x132b/0x38e0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:5148
alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab mm/slub.c:2660 [inline]
new_slab+0x247/0x330 mm/slub.c:2714
___slab_alloc+0xcf2/0x1750 mm/slub.c:3901
__slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3992
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]
__kmalloc_cache_noprof+0xfb/0x3e0 mm/slub.c:4402
kmalloc_noprof include/linux/slab.h:905 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
device_private_init drivers/base/core.c:3534 [inline]
device_add+0xccc/0x1aa0 drivers/base/core.c:3585
snd_register_device+0x328/0x4d0 sound/core/sound.c:278
snd_ctl_dev_register+0x77/0x1b0 sound/core/control.c:2296
__snd_device_register sound/core/device.c:149 [inline]
snd_device_register_all+0x10f/0x1b0 sound/core/device.c:197
snd_card_register+0x106/0x7c0 sound/core/init.c:893
try_to_register_card+0x1d7/0x370 sound/usb/card.c:856
usb_audio_probe+0xe96/0x3cf0 sound/usb/card.c:1025
usb_probe_interface+0x303/0xa40 drivers/usb/core/driver.c:396
page last free pid 6554 tgid 6553 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0x7d5/0x10f0 mm/page_alloc.c:2895
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x4d/0x120 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:340
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4191 [inline]
slab_alloc_node mm/slub.c:4240 [inline]
__kmalloc_cache_noprof+0x1f1/0x3e0 mm/slub.c:4402
kmalloc_noprof include/linux/slab.h:905 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
dev_new drivers/usb/gadget/legacy/raw_gadget.c:192 [inline]
raw_open+0x8b/0x500 drivers/usb/gadget/legacy/raw_gadget.c:434
misc_open+0x35d/0x420 drivers/char/misc.c:161
chrdev_open+0x234/0x6a0 fs/char_dev.c:414
do_dentry_open+0x982/0x1530 fs/open.c:965
vfs_open+0x82/0x3f0 fs/open.c:1095
do_open fs/namei.c:3887 [inline]
path_openat+0x1de4/0x2cb0 fs/namei.c:4046
do_filp_open+0x20b/0x470 fs/namei.c:4073
do_sys_openat2+0x11b/0x1d0 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_openat fs/open.c:1466 [inline]
__se_sys_openat fs/open.c:1461 [inline]
__x64_sys_openat+0x174/0x210 fs/open.c:1461
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88805cb67800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88805cb67880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88805cb67900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88805cb67980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88805cb67a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

----------------
Code disassembly (best guess):

0: 00 e8 add %ch,%al
2: b2 d3 mov $0xd3,%dl
4: 28 00 sub %al,(%rax)
6: 9c pushf
7: 5b pop %rbx
8: 81 e3 00 02 00 00 and $0x200,%ebx
e: 31 ff xor %edi,%edi
10: 48 89 de mov %rbx,%rsi
13: e8 30 e8 20 00 call 0x20e848
18: 48 85 db test %rbx,%rbx
1b: 0f 85 55 01 00 00 jne 0x176
21: e8 b2 ec 20 00 call 0x20ecd8
26: fb sti
27: 4c 89 e0 mov %r12,%rax
* 2a: 48 c1 e8 03 shr $0x3,%rax <-- trapping instruction
2e: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1)
33: 0f 84 11 ff ff ff je 0xffffff4a
39: 4c 89 e7 mov %r12,%rdi
3c: e8 .byte 0xe8
3d: 67 5f addr32 pop %rdi
3f: 86 .byte 0x86


Tested on:

commit: cec1e6e5 Merge tag 'sched_ext-for-6.17-rc7-fixes' of g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=176338e2580000

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=12fad712580000

[Alan Stern]

On Tue, Sep 23, 2025 at 04:47:20AM +0530, Brahmajit Das wrote:
> Syzkaller reported a general protection fault in snd_usbmidi_do_output(),
> caused by dereferencing a NULL URB pointer when accessing
> ep->urbs[urb_index].urb.
>
> This can happen in rare race conditions where the URB was not initialized
> or was already freed (e.g. during disconnect or after errors), and the
> output timer or other path tries to reuse it.
>
> Fix this by checking if the URB is NULL before accessing it, and skipping
> the current slot if it is.
>
> Reported-by: syzbot+f02665...@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?extid=f02665daa2abeef4a947
>
> Signed-off-by: Brahmajit Das <lis...@listout.xyz>
> ---
> sound/usb/midi.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/sound/usb/midi.c b/sound/usb/midi.c
> index acb3bf92857c..7919a39decb4 100644
> --- a/sound/usb/midi.c
> +++ b/sound/usb/midi.c
> @@ -307,6 +307,10 @@ static void snd_usbmidi_do_output(struct snd_usb_midi_out_endpoint *ep)

> for (;;) {
> if (!(ep->active_urbs & (1 << urb_index))) {
> urb = ep->urbs[urb_index].urb;
> + if (!urb) {

> + // Skip this urb
> + goto next_urb;
> + }

What prevents the URB from being freed right here? If this happens,
the code below would access memory that was deallocated.

To prevent races, you have to use some sort of lock or other
synchronization mechanism. A simple test won't work.

Alan Stern

> urb->transfer_buffer_length = 0;
> ep->umidi->usb_protocol_ops->output(ep, urb);
> if (urb->transfer_buffer_length == 0)

> @@ -319,6 +323,7 @@ static void snd_usbmidi_do_output(struct snd_usb_midi_out_endpoint *ep)

> break;
> ep->active_urbs |= 1 << urb_index;
> }

> +next_urb:

> if (++urb_index >= OUTPUT_URBS)
> urb_index = 0;
> if (urb_index == ep->next_urb)

> --
> 2.51.0

[Takashi Iwai]

Yes. The timer instance itself should have been killed before
releasing the resources.

I guess the patch below could cover it, but since I'm traveling, I
can't check it for now. Will check later once after I'm back.


thanks,

Takashi

--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1511,6 +1511,7 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
{
int i;

+ timer_shutdown_sync(&umidi->error_timer);
for (i = 0; i < MIDI_MAX_ENDPOINTS; ++i) {
struct snd_usb_midi_endpoint *ep = &umidi->endpoints[i];
if (ep->out)
@@ -1519,7 +1520,6 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
snd_usbmidi_in_endpoint_delete(ep->in);
}
mutex_destroy(&umidi->mutex);
- timer_shutdown_sync(&umidi->error_timer);
kfree(umidi);
}

[Brahmajit Das]

[Brahmajit Das]

[Hillf Danton]

> Date: Mon, 22 Sep 2025 09:54:28 -0700 [thread overview]

> 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

#syz test upstream master

--- x/sound/usb/midi.c
+++ y/sound/usb/midi.c
@@ -307,6 +307,8 @@ static void snd_usbmidi_do_output(struct

for (;;) {
if (!(ep->active_urbs & (1 << urb_index))) {
urb = ep->urbs[urb_index].urb;
+ if (!urb)

+ goto next;

urb->transfer_buffer_length = 0;
ep->umidi->usb_protocol_ops->output(ep, urb);
if (urb->transfer_buffer_length == 0)

@@ -319,6 +321,7 @@ static void snd_usbmidi_do_output(struct

break;
ep->active_urbs |= 1 << urb_index;
}

+ next:

if (++urb_index >= OUTPUT_URBS)
urb_index = 0;
if (urb_index == ep->next_urb)

@@ -1396,13 +1399,19 @@ static int snd_usbmidi_in_endpoint_creat
static void snd_usbmidi_out_endpoint_clear(struct snd_usb_midi_out_endpoint *ep)
{
unsigned int i;
+ unsigned long flags;

+ spin_lock_irqsave(&ep->buffer_lock, flags);
for (i = 0; i < OUTPUT_URBS; ++i)
if (ep->urbs[i].urb) {
- free_urb_and_buffer(ep->umidi, ep->urbs[i].urb,
- ep->max_transfer);
+ struct urb *urb = ep->urbs[i].urb;
+
ep->urbs[i].urb = NULL;
+ spin_unlock_irqrestore(&ep->buffer_lock, flags);
+ free_urb_and_buffer(ep->umidi, urb, ep->max_transfer);
+ spin_lock_irqsave(&ep->buffer_lock, flags);
}
+ spin_unlock_irqrestore(&ep->buffer_lock, flags);
}

static void snd_usbmidi_out_endpoint_delete(struct snd_usb_midi_out_endpoint *ep)

@@ -1522,15 +1531,23 @@ static void snd_usbmidi_free(struct snd_

{
int i;

+ timer_shutdown_sync(&umidi->error_timer);
for (i = 0; i < MIDI_MAX_ENDPOINTS; ++i) {
struct snd_usb_midi_endpoint *ep = &umidi->endpoints[i];

- if (ep->out)
+ int j;
+
+ if (ep->out) {
+ for (j = 0; j < OUTPUT_URBS; ++j)
+ usb_kill_urb(ep->out->urbs[j].urb);
snd_usbmidi_out_endpoint_delete(ep->out);
- if (ep->in)
+ }
+ if (ep->in) {
+ for (j = 0; j < INPUT_URBS; ++j)
+ usb_kill_urb(ep->in->urbs[j]);
snd_usbmidi_in_endpoint_delete(ep->in);
+ }

}
mutex_destroy(&umidi->mutex);
- timer_shutdown_sync(&umidi->error_timer);
kfree(umidi);
}

--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+f02665...@syzkaller.appspotmail.com
Tested-by: syzbot+f02665...@syzkaller.appspotmail.com

Tested on:

commit: cec1e6e5 Merge tag 'sched_ext-for-6.17-rc7-fixes' of g..

git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=116b04e2580000

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=13f34142580000

Note: testing is done by a robot and is best-effort only.