Message-ID: <20251222022859.1691-1-hdanton@sina.com>
Date: Mon, 22 Dec 2025 10:28:57 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+addf1973f8732e2cc468@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	linux-sound@...r.kernel.org,
	perex@...ex.cz,
	syzkaller-bugs@...glegroups.com,
	tiwai@...e.com
Subject: Re: [syzbot] [sound?] KASAN: slab-use-after-free Read in snd_pcm_action

Date: Sun, 21 Dec 2025 16:11:22 -0800
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    9094662f6707 Merge tag 'ata-6.19-rc2' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1568ddb4580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1f2b6fe1fdf1a00b
> dashboard link: https://syzkaller.appspot.com/bug?extid=addf1973f8732e2cc468
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13b343c2580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1762db1a580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/024031cc0ef1/disk-9094662f.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ba00f3b9b8e7/vmlinux-9094662f.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/a92db982c114/bzImage-9094662f.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+addf1973f8732e2cc468@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in rt_spin_lock+0x88/0x3e0 kernel/locking/spinlock_rt.c:56
> Read of size 1 at addr ffff888034ea7200 by task syz.1.1236/9742
> 
> CPU: 1 UID: 0 PID: 9742 Comm: syz.1.1236 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0xe8/0x150 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
>  __kasan_check_byte+0x2a/0x40 mm/kasan/common.c:573
>  kasan_check_byte include/linux/kasan.h:401 [inline]
>  lock_acquire+0x84/0x340 kernel/locking/lockdep.c:5842
>  rt_spin_lock+0x88/0x3e0 kernel/locking/spinlock_rt.c:56
>  spin_lock include/linux/spinlock_rt.h:44 [inline]
>  __wake_up_common_lock+0x2f/0x1e0 kernel/sched/wait.c:124
>  snd_pcm_action_single sound/core/pcm_native.c:-1 [inline]
>  snd_pcm_action+0x1f4/0x240 sound/core/pcm_native.c:1393
>  loopback_check_format sound/drivers/aloop.c:363 [inline]
>  loopback_trigger+0xb82/0x1b60 sound/drivers/aloop.c:411
>  snd_pcm_do_start+0xb7/0x180 sound/core/pcm_native.c:1454
>  snd_pcm_action_single sound/core/pcm_native.c:1310 [inline]
>  snd_pcm_action+0xe7/0x240 sound/core/pcm_native.c:1393
>  __snd_pcm_lib_xfer+0x1762/0x1d00 sound/core/pcm_lib.c:2405
>  snd_pcm_oss_write3+0x1bc/0x350 sound/core/oss/pcm_oss.c:1241
>  snd_pcm_plug_write_transfer+0x2cb/0x4c0 sound/core/oss/pcm_plugin.c:630
>  snd_pcm_oss_write2 sound/core/oss/pcm_oss.c:1373 [inline]
>  snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1439 [inline]
>  snd_pcm_oss_write+0xa31/0xf20 sound/core/oss/pcm_oss.c:2794

What is weird is why snd_pcm_oss_write failed to block snd_pcm_oss_release
in file_operations POV. By weird I mean file can not be closed with a writer.

>  vfs_write+0x287/0xb40 fs/read_write.c:684
>  ksys_write+0x14b/0x260 fs/read_write.c:738
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f1277acf749
> 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:00007f1277115038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007f1277d26090 RCX: 00007f1277acf749
> RDX: 0000000000004000 RSI: 00002000000012c0 RDI: 0000000000000008
> RBP: 00007f1277b53f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f1277d26128 R14: 00007f1277d26090 R15: 00007ffea9722d18
>  </TASK>
> 
> Allocated by task 9740:
>  kasan_save_stack mm/kasan/common.c:56 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
>  poison_kmalloc_redzone mm/kasan/common.c:397 [inline]
>  __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:414
>  kasan_kmalloc include/linux/kasan.h:262 [inline]
>  __kmalloc_cache_noprof+0x1fb/0x6d0 mm/slub.c:5776
>  kmalloc_noprof include/linux/slab.h:957 [inline]
>  kzalloc_noprof include/linux/slab.h:1094 [inline]
>  snd_pcm_attach_substream+0x5b7/0xb30 sound/core/pcm.c:938
>  snd_pcm_open_substream+0xb6/0x2410 sound/core/pcm_native.c:2756
>  snd_pcm_oss_open_file sound/core/oss/pcm_oss.c:2437 [inline]
>  snd_pcm_oss_open+0xf2a/0x1bd0 sound/core/oss/pcm_oss.c:2518
>  chrdev_open+0x4cf/0x5e0 fs/char_dev.c:414
>  do_dentry_open+0x7d0/0x1270 fs/open.c:962
>  vfs_open+0x3b/0x350 fs/open.c:1094
>  do_open fs/namei.c:4628 [inline]
>  path_openat+0x342a/0x3df0 fs/namei.c:4787
>  do_filp_open+0x1fa/0x410 fs/namei.c:4814
>  do_sys_openat2+0x121/0x200 fs/open.c:1430
>  do_sys_open fs/open.c:1436 [inline]
>  __do_sys_openat fs/open.c:1452 [inline]
>  __se_sys_openat fs/open.c:1447 [inline]
>  __x64_sys_openat+0x138/0x170 fs/open.c:1447
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Freed by task 9740:
>  kasan_save_stack mm/kasan/common.c:56 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
>  kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
>  poison_slab_object mm/kasan/common.c:252 [inline]
>  __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284
>  kasan_slab_free include/linux/kasan.h:234 [inline]
>  slab_free_hook mm/slub.c:2540 [inline]
>  slab_free mm/slub.c:6670 [inline]
>  kfree+0x1bd/0x900 mm/slub.c:6878
>  snd_pcm_detach_substream+0x1e1/0x290 sound/core/pcm.c:1003
>  snd_pcm_oss_release_file sound/core/oss/pcm_oss.c:2396 [inline]
>  snd_pcm_oss_release+0x184/0x250 sound/core/oss/pcm_oss.c:2575
>  __fput+0x45b/0xa80 fs/file_table.c:468
>  task_work_run+0x1d4/0x260 kernel/task_work.c:233
>  get_signal+0x11c4/0x1310 kernel/signal.c:2807
>  arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337
>  __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
>  exit_to_user_mode_loop+0x87/0x4e0 kernel/entry/common.c:75
>  __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
>  syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
>  syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
>  syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
>  do_syscall_64+0x2b7/0xf80 arch/x86/entry/syscall_64.c:100
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> The buggy address belongs to the object at ffff888034ea7000
>  which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 512 bytes inside of
>  freed 2048-byte region [ffff888034ea7000, ffff888034ea7800)
> 
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x34ea0
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> flags: 0x80000000000040(head|node=0|zone=1)
> page_type: f5(slab)
> raw: 0080000000000040 ffff88813ff27000 dead000000000100 dead000000000122
> raw: 0000000000000000 0000000000080008 00000000f5000000 0000000000000000
> head: 0080000000000040 ffff88813ff27000 dead000000000100 dead000000000122
> head: 0000000000000000 0000000000080008 00000000f5000000 0000000000000000
> head: 0080000000000003 ffffea0000d3a801 00000000ffffffff 00000000ffffffff
> head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000008
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd28c0(GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5917, tgid 5917 (syz-executor), ts 127811454833, free_ts 125843464373
>  set_page_owner include/linux/page_owner.h:32 [inline]
>  post_alloc_hook+0x234/0x290 mm/page_alloc.c:1846
>  prep_new_page mm/page_alloc.c:1854 [inline]
>  get_page_from_freelist+0x28c0/0x2960 mm/page_alloc.c:3915
>  __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
>  alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2486
>  alloc_slab_page mm/slub.c:3075 [inline]
>  allocate_slab+0x86/0x3b0 mm/slub.c:3248
>  new_slab mm/slub.c:3302 [inline]
>  ___slab_alloc+0xb10/0x13e0 mm/slub.c:4656
>  __slab_alloc+0xc6/0x1f0 mm/slub.c:4779
>  __slab_alloc_node mm/slub.c:4855 [inline]
>  slab_alloc_node mm/slub.c:5251 [inline]
>  __do_kmalloc_node mm/slub.c:5656 [inline]
>  __kmalloc_node_track_caller_noprof+0x2bf/0x810 mm/slub.c:5764
>  kmalloc_reserve+0x136/0x290 net/core/skbuff.c:608
>  pskb_expand_head+0x19d/0x1160 net/core/skbuff.c:2282
>  netlink_trim+0x1b3/0x2c0 net/netlink/af_netlink.c:1299
>  netlink_broadcast_filtered+0xd6/0x1000 net/netlink/af_netlink.c:1512
>  nlmsg_multicast_filtered include/net/netlink.h:1165 [inline]
>  nlmsg_multicast include/net/netlink.h:1184 [inline]
>  nlmsg_notify+0xf0/0x1a0 net/netlink/af_netlink.c:2593
>  rtnl_notify net/core/rtnetlink.c:958 [inline]
>  rtmsg_ifinfo_send net/core/rtnetlink.c:4436 [inline]
>  rtmsg_ifinfo_event net/core/rtnetlink.c:4452 [inline]
>  rtnetlink_event+0x224/0x270 net/core/rtnetlink.c:7018
>  notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
>  call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
>  call_netdevice_notifiers net/core/dev.c:2282 [inline]
>  netif_change_name+0x5db/0x970 net/core/dev.c:1490
> page last free pid 5966 tgid 5966 stack trace:
>  reset_page_owner include/linux/page_owner.h:25 [inline]
>  free_pages_prepare mm/page_alloc.c:1395 [inline]
>  __free_frozen_pages+0xfe1/0x1170 mm/page_alloc.c:2943
>  discard_slab mm/slub.c:3346 [inline]
>  __put_partials+0x149/0x170 mm/slub.c:3886
>  __slab_free+0x2af/0x330 mm/slub.c:5952
>  qlink_free mm/kasan/quarantine.c:163 [inline]
>  qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
>  kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
>  __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:349
>  kasan_slab_alloc include/linux/kasan.h:252 [inline]
>  slab_post_alloc_hook mm/slub.c:4953 [inline]
>  slab_alloc_node mm/slub.c:5263 [inline]
>  kmem_cache_alloc_noprof+0x18d/0x6c0 mm/slub.c:5270
>  getname_flags+0xb8/0x540 fs/namei.c:146
>  user_path_at+0x24/0x60 fs/namei.c:3566
>  user_statfs+0x94/0x170 fs/statfs.c:103
>  __do_sys_statfs fs/statfs.c:193 [inline]
>  __se_sys_statfs fs/statfs.c:190 [inline]
>  __x64_sys_statfs+0xe0/0x1b0 fs/statfs.c:190
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Memory state around the buggy address:
>  ffff888034ea7100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888034ea7180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff888034ea7200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                    ^
>  ffff888034ea7280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888034ea7300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

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