Re: [syzbot] [sound?] KASAN: slab-use-after-free Read in snd_usbmidi_error_timer (2)

[Takashi Iwai <tiwai@suse.de>]

On Wed, 24 Sep 2025 07:35:35 +0200,
syzbot wrote:
> 
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    cec1e6e5d1ab Merge tag 'sched_ext-for-6.17-rc7-fixes' of g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=127fc142580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4d8792ecb6308d0f
> dashboard link: https://syzkaller.appspot.com/bug?extid=ce952c05d40571083fd6
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f000e10907d9/disk-cec1e6e5.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/e8da77cc2298/vmlinux-cec1e6e5.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9ad6164e7d28/bzImage-cec1e6e5.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ce952c05d40571083fd6@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline]
> BUG: KASAN: slab-use-after-free in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
> BUG: KASAN: slab-use-after-free in snd_usbmidi_error_timer+0x15d/0x660 sound/usb/midi.c:355
> Read of size 4 at addr ffff8880310f9a10 by task syz.4.2001/13191
> 
> CPU: 0 UID: 0 PID: 13191 Comm: syz.4.2001 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
> Call Trace:
>  <IRQ>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  print_address_description mm/kasan/report.c:378 [inline]
>  print_report+0xca/0x240 mm/kasan/report.c:482
>  kasan_report+0x118/0x150 mm/kasan/report.c:595
>  check_region_inline mm/kasan/generic.c:-1 [inline]
>  kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:189
>  instrument_atomic_read include/linux/instrumented.h:68 [inline]
>  atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
>  snd_usbmidi_error_timer+0x15d/0x660 sound/usb/midi.c:355
>  call_timer_fn+0x17b/0x5f0 kernel/time/timer.c:1747
>  expire_timers kernel/time/timer.c:1798 [inline]
>  __run_timers kernel/time/timer.c:2372 [inline]
>  __run_timer_base+0x61a/0x860 kernel/time/timer.c:2384
>  run_timer_base kernel/time/timer.c:2393 [inline]
>  run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403
>  handle_softirqs+0x283/0x870 kernel/softirq.c:579
>  __do_softirq kernel/softirq.c:613 [inline]
>  invoke_softirq kernel/softirq.c:453 [inline]
>  __irq_exit_rcu+0xca/0x1f0 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+0xa6/0xc0 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:__sanitizer_cov_trace_pc+0x46/0x70 kernel/kcov.c:222
> Code: ff 00 74 11 81 fa 00 01 00 00 75 35 83 b9 3c 16 00 00 00 74 2c 8b 91 18 16 00 00 83 fa 02 75 21 48 8b 91 20 16 00 00 48 8b 32 <48> 8d 7e 01 8b 89 1c 16 00 00 48 39 cf 73 08 48 89 3a 48 89 44 f2
> RSP: 0018:ffffc90003007658 EFLAGS: 00000246
> RAX: ffffffff8b72d1aa RBX: ffffc900030077c0 RCX: ffff88802acd3c00
> RDX: ffffc9000d3ed000 RSI: 000000000007ffff RDI: ffffffff8be33f20
> RBP: ffffc90003007790 R08: 0000000000000000 R09: ffffffff8b72d15c
> R10: dffffc0000000000 R11: fffffbfff1f47507 R12: dffffc0000000000
> R13: 1ffff92000600ed4 R14: 0000000000000001 R15: ffffc900030076c0
>  rcu_read_lock include/linux/rcupdate.h:842 [inline]
>  mt_find+0x1aa/0x5f0 lib/maple_tree.c:6931
>  find_vma+0xe7/0x160 mm/mmap.c:909
>  lock_mm_and_find_vma+0x5f/0x300 mm/mmap_lock.c:340
>  do_user_addr_fault+0x331/0x1390 arch/x86/mm/fault.c:1359
>  handle_page_fault arch/x86/mm/fault.c:1476 [inline]
>  exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
>  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
> RIP: 0010:rep_movs_alternative+0x30/0x90 arch/x86/lib/copy_user_64.S:60
> Code: 83 f9 08 73 25 85 c9 74 0f 8a 06 88 07 48 ff c7 48 ff c6 48 ff c9 75 f1 e9 8d 0a 04 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 <48> 8b 06 48 89 07 48 83 c6 08 48 83 c7 08 83 e9 08 74 db 83 f9 08
> RSP: 0018:ffffc90003007a18 EFLAGS: 00050206
> RAX: 00007ffffffff001 RBX: 0000000000000038 RCX: 0000000000000038
> RDX: 0000000000000001 RSI: 0000200000297000 RDI: ffffc90003007aa0
> RBP: ffffc90003007c30 R08: ffffc90003007ad7 R09: 1ffff92000600f5a
> R10: dffffc0000000000 R11: fffff52000600f5b R12: 0000000000000002
> R13: dffffc0000000000 R14: ffffc90003007aa0 R15: 0000200000297000
>  copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
>  raw_copy_from_user arch/x86/include/asm/uaccess_64.h:141 [inline]
>  _inline_copy_from_user include/linux/uaccess.h:178 [inline]
>  _copy_from_user+0x7a/0xb0 lib/usercopy.c:18
>  copy_from_user include/linux/uaccess.h:212 [inline]
>  copy_msghdr_from_user net/socket.c:2544 [inline]
>  recvmsg_copy_msghdr net/socket.c:2800 [inline]
>  ___sys_recvmsg+0x12e/0x510 net/socket.c:2872
>  do_recvmmsg+0x307/0x770 net/socket.c:2971
>  __sys_recvmmsg net/socket.c:3045 [inline]
>  __do_sys_recvmmsg net/socket.c:3068 [inline]
>  __se_sys_recvmmsg net/socket.c:3061 [inline]
>  __x64_sys_recvmmsg+0x190/0x240 net/socket.c:3061
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f873778eec9
> 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:00007f87359f6038 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
> RAX: ffffffffffffffda RBX: 00007f87379e6090 RCX: 00007f873778eec9
> RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000003
> RBP: 00007f8737811f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f87379e6128 R14: 00007f87379e6090 R15: 00007f8737b0fa28
>  </TASK>
> 
> Allocated by task 5950:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>  poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
>  __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
>  kasan_kmalloc include/linux/kasan.h:260 [inline]
>  __do_kmalloc_node mm/slub.c:4376 [inline]
>  __kmalloc_noprof+0x27a/0x4f0 mm/slub.c:4388
>  kmalloc_noprof include/linux/slab.h:909 [inline]
>  usb_alloc_urb+0x46/0x150 drivers/usb/core/urb.c:75
>  snd_usbmidi_in_endpoint_create+0xb4/0xa30 sound/usb/midi.c:1348
>  snd_usbmidi_create_endpoints_midiman sound/usb/midi.c:2363 [inline]
>  __snd_usbmidi_create+0x2223/0x2a70 sound/usb/midi.c:2646
>  snd_usb_midi_v2_create+0x43e6/0x4660 sound/usb/midi2.c:1178
>  usb_audio_probe+0xb78/0x1e10 sound/usb/card.c:976
>  usb_probe_interface+0x668/0xc30 drivers/usb/core/driver.c:396
>  call_driver_probe drivers/base/dd.c:-1 [inline]
>  really_probe+0x26a/0x9e0 drivers/base/dd.c:659
>  __driver_probe_device+0x18c/0x2f0 drivers/base/dd.c:801
>  driver_probe_device+0x4f/0x430 drivers/base/dd.c:831
>  __device_attach_driver+0x2ce/0x530 drivers/base/dd.c:959
>  bus_for_each_drv+0x251/0x2e0 drivers/base/bus.c:462
>  __device_attach+0x2b8/0x400 drivers/base/dd.c:1031
>  bus_probe_device+0x185/0x260 drivers/base/bus.c:537
>  device_add+0x7b6/0xb50 drivers/base/core.c:3689
>  usb_set_configuration+0x1a87/0x20e0 drivers/usb/core/message.c:2210
>  usb_generic_driver_probe+0x8d/0x150 drivers/usb/core/generic.c:250
>  usb_probe_device+0x1c4/0x390 drivers/usb/core/driver.c:291
>  call_driver_probe drivers/base/dd.c:-1 [inline]
>  really_probe+0x26a/0x9e0 drivers/base/dd.c:659
>  __driver_probe_device+0x18c/0x2f0 drivers/base/dd.c:801
>  driver_probe_device+0x4f/0x430 drivers/base/dd.c:831
>  __device_attach_driver+0x2ce/0x530 drivers/base/dd.c:959
>  bus_for_each_drv+0x251/0x2e0 drivers/base/bus.c:462
>  __device_attach+0x2b8/0x400 drivers/base/dd.c:1031
>  bus_probe_device+0x185/0x260 drivers/base/bus.c:537
>  device_add+0x7b6/0xb50 drivers/base/core.c:3689
>  usb_new_device+0xa39/0x16f0 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+0x2958/0x4a20 drivers/usb/core/hub.c:5952
>  process_one_work kernel/workqueue.c:3236 [inline]
>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
>  kthread+0x70e/0x8a0 kernel/kthread.c:463
>  ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> 
> Freed by task 5950:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>  kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
>  poison_slab_object mm/kasan/common.c:243 [inline]
>  __kasan_slab_free+0x5b/0x80 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+0x18e/0x440 mm/slub.c:4894
>  free_urb_and_buffer sound/usb/midi.c:1309 [inline]
>  snd_usbmidi_in_endpoint_delete+0xde/0x680 sound/usb/midi.c:1322
>  snd_usbmidi_free sound/usb/midi.c:1530 [inline]
>  snd_usbmidi_rawmidi_free+0xae/0x160 sound/usb/midi.c:1591
>  snd_rawmidi_free+0x3bc/0x410 sound/core/rawmidi.c:1934
>  snd_rawmidi_dev_free+0x38/0x50 sound/core/rawmidi.c:1945
>  __snd_device_free+0x1d2/0x2e0 sound/core/device.c:76
>  snd_device_free_all+0xcf/0x180 sound/core/device.c:233
>  snd_card_do_free sound/core/init.c:587 [inline]
>  release_card_device+0x75/0x1b0 sound/core/init.c:153
>  device_release+0x9c/0x1c0 drivers/base/core.c:-1
>  kobject_cleanup lib/kobject.c:689 [inline]
>  kobject_release lib/kobject.c:720 [inline]
>  kref_put include/linux/kref.h:65 [inline]
>  kobject_put+0x22b/0x480 lib/kobject.c:737
>  snd_card_free_when_closed sound/core/init.c:618 [inline]
>  snd_card_free+0x110/0x190 sound/core/init.c:650
>  usb_audio_probe+0x193f/0x1e10 sound/usb/card.c:1034
>  usb_probe_interface+0x668/0xc30 drivers/usb/core/driver.c:396
>  call_driver_probe drivers/base/dd.c:-1 [inline]
>  really_probe+0x26a/0x9e0 drivers/base/dd.c:659
>  __driver_probe_device+0x18c/0x2f0 drivers/base/dd.c:801
>  driver_probe_device+0x4f/0x430 drivers/base/dd.c:831
>  __device_attach_driver+0x2ce/0x530 drivers/base/dd.c:959
>  bus_for_each_drv+0x251/0x2e0 drivers/base/bus.c:462
>  __device_attach+0x2b8/0x400 drivers/base/dd.c:1031
>  bus_probe_device+0x185/0x260 drivers/base/bus.c:537
>  device_add+0x7b6/0xb50 drivers/base/core.c:3689
>  usb_set_configuration+0x1a87/0x20e0 drivers/usb/core/message.c:2210
>  usb_generic_driver_probe+0x8d/0x150 drivers/usb/core/generic.c:250
>  usb_probe_device+0x1c4/0x390 drivers/usb/core/driver.c:291
>  call_driver_probe drivers/base/dd.c:-1 [inline]
>  really_probe+0x26a/0x9e0 drivers/base/dd.c:659
>  __driver_probe_device+0x18c/0x2f0 drivers/base/dd.c:801
>  driver_probe_device+0x4f/0x430 drivers/base/dd.c:831
>  __device_attach_driver+0x2ce/0x530 drivers/base/dd.c:959
>  bus_for_each_drv+0x251/0x2e0 drivers/base/bus.c:462
>  __device_attach+0x2b8/0x400 drivers/base/dd.c:1031
>  bus_probe_device+0x185/0x260 drivers/base/bus.c:537
>  device_add+0x7b6/0xb50 drivers/base/core.c:3689
>  usb_new_device+0xa39/0x16f0 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+0x2958/0x4a20 drivers/usb/core/hub.c:5952
>  process_one_work kernel/workqueue.c:3236 [inline]
>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
>  kthread+0x70e/0x8a0 kernel/kthread.c:463
>  ret_from_fork+0x439/0x7d0 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 ffff8880310f9a00
>  which belongs to the cache kmalloc-192 of size 192
> The buggy address is located 16 bytes inside of
>  freed 192-byte region [ffff8880310f9a00, ffff8880310f9ac0)
> 
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x310f9
> anon flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 00fff00000000000 ffff88801a4413c0 0000000000000000 dead000000000001
> raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 1, tgid 1 (swapper/0), ts 19362280210, free_ts 19332206122
>  set_page_owner include/linux/page_owner.h:32 [inline]
>  post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
>  prep_new_page mm/page_alloc.c:1859 [inline]
>  get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858
>  __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
>  alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
>  alloc_slab_page mm/slub.c:2492 [inline]
>  allocate_slab+0x8a/0x370 mm/slub.c:2660
>  new_slab mm/slub.c:2714 [inline]
>  ___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
>  __slab_alloc mm/slub.c:3992 [inline]
>  __slab_alloc_node mm/slub.c:4067 [inline]
>  slab_alloc_node mm/slub.c:4228 [inline]
>  __kmalloc_cache_noprof+0x296/0x3d0 mm/slub.c:4402
>  kmalloc_noprof include/linux/slab.h:905 [inline]
>  kzalloc_noprof include/linux/slab.h:1039 [inline]
>  call_usermodehelper_setup+0x8e/0x270 kernel/umh.c:362
>  kobject_uevent_env+0x65c/0x8c0 lib/kobject_uevent.c:628
>  kernel_add_sysfs_param+0xb1/0xe0 kernel/params.c:816
>  param_sysfs_builtin+0x18a/0x230 kernel/params.c:851
>  param_sysfs_builtin_init+0x23/0x30 kernel/params.c:987
>  do_one_initcall+0x233/0x820 init/main.c:1269
>  do_initcall_level+0x104/0x190 init/main.c:1331
>  do_initcalls+0x59/0xa0 init/main.c:1347
>  kernel_init_freeable+0x334/0x4b0 init/main.c:1579
> page last free pid 980 tgid 980 stack trace:
>  reset_page_owner include/linux/page_owner.h:25 [inline]
>  free_pages_prepare mm/page_alloc.c:1395 [inline]
>  __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2895
>  vfree+0x25a/0x400 mm/vmalloc.c:3434
>  delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3353
>  process_one_work kernel/workqueue.c:3236 [inline]
>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
>  kthread+0x70e/0x8a0 kernel/kthread.c:463
>  ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> 
> Memory state around the buggy address:
>  ffff8880310f9900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff8880310f9980: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff8880310f9a00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                          ^
>  ffff8880310f9a80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8880310f9b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ==================================================================
> ----------------
> Code disassembly (best guess):
>    0:	ff 00                	incl   (%rax)
>    2:	74 11                	je     0x15
>    4:	81 fa 00 01 00 00    	cmp    $0x100,%edx
>    a:	75 35                	jne    0x41
>    c:	83 b9 3c 16 00 00 00 	cmpl   $0x0,0x163c(%rcx)
>   13:	74 2c                	je     0x41
>   15:	8b 91 18 16 00 00    	mov    0x1618(%rcx),%edx
>   1b:	83 fa 02             	cmp    $0x2,%edx
>   1e:	75 21                	jne    0x41
>   20:	48 8b 91 20 16 00 00 	mov    0x1620(%rcx),%rdx
>   27:	48 8b 32             	mov    (%rdx),%rsi
> * 2a:	48 8d 7e 01          	lea    0x1(%rsi),%rdi <-- trapping instruction
>   2e:	8b 89 1c 16 00 00    	mov    0x161c(%rcx),%ecx
>   34:	48 39 cf             	cmp    %rcx,%rdi
>   37:	73 08                	jae    0x41
>   39:	48 89 3a             	mov    %rdi,(%rdx)
>   3c:	48                   	rex.W
>   3d:	89                   	.byte 0x89
>   3e:	44                   	rex.R
>   3f:	f2                   	repnz
> 
> 
> ---
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#syz fix: ALSA: usb-audio: fix race condition to UAF in snd_usbmidi_free