Forwarded: Re: [PATCH v1] Bluetooth: hci_sync: Fix UAF in le_read_features_complete

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Subject: Re: [PATCH v1] Bluetooth: hci_sync: Fix UAF in le_read_features_complete
Author: luiz.dentz@xxxxxxxxx

#syz test

On Wed, Mar 25, 2026 at 11:43 AM Luiz Augusto von Dentz
<luiz.dentz@xxxxxxxxx> wrote:
>
> ---------- Forwarded message ---------
> From: Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx>
> Date: Wed, Mar 25, 2026 at 11:18 AM
> Subject: [PATCH v1] Bluetooth: hci_sync: Fix UAF in le_read_features_complete
> To: <linux-bluetooth@xxxxxxxxxxxxxxx>
>
>
> From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
>
> This fixes the following backtrace caused by hci_conn being freed
> before le_read_features_complete but after
> hci_le_read_remote_features_sync so hci_conn_del -> hci_cmd_sync_dequeue
> is not able to prevent it:
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in instrument_atomic_read_write
> include/linux/instrumented.h:96 [inline]
> BUG: KASAN: slab-use-after-free in atomic_dec_and_test
> include/linux/atomic/atomic-instrumented.h:1383 [inline]
> BUG: KASAN: slab-use-after-free in hci_conn_drop
> include/net/bluetooth/hci_core.h:1688 [inline]
> BUG: KASAN: slab-use-after-free in
> le_read_features_complete+0x5b/0x340 net/bluetooth/hci_sync.c:7344
> Write of size 4 at addr ffff8880796b0010 by task kworker/u9:0/52
>
> CPU: 0 UID: 0 PID: 52 Comm: kworker/u9:0 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 10/25/2025
> Workqueue: hci0 hci_cmd_sync_work
> Call Trace:
>  <TASK>
>  __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
>  check_region_inline mm/kasan/generic.c:194 [inline]
>  kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:200
>  instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
>  atomic_dec_and_test include/linux/atomic/atomic-instrumented.h:1383 [inline]
>  hci_conn_drop include/net/bluetooth/hci_core.h:1688 [inline]
>  le_read_features_complete+0x5b/0x340 net/bluetooth/hci_sync.c:7344
>  hci_cmd_sync_work+0x1ff/0x430 net/bluetooth/hci_sync.c:334
>  process_one_work+0x9ba/0x1b20 kernel/workqueue.c:3257
>  process_scheduled_works kernel/workqueue.c:3340 [inline]
>  worker_thread+0x6c8/0xf10 kernel/workqueue.c:3421
>  kthread+0x3c5/0x780 kernel/kthread.c:463
>  ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
>  </TASK>
>
> Allocated by task 5932:
>  kasan_save_stack+0x33/0x60 mm/kasan/common.c:56
>  kasan_save_track+0x14/0x30 mm/kasan/common.c:77
>  poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
>  __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:417
>  kmalloc_noprof include/linux/slab.h:957 [inline]
>  kzalloc_noprof include/linux/slab.h:1094 [inline]
>  __hci_conn_add+0xf8/0x1c70 net/bluetooth/hci_conn.c:963
>  hci_conn_add_unset+0x76/0x100 net/bluetooth/hci_conn.c:1084
>  le_conn_complete_evt+0x639/0x1f20 net/bluetooth/hci_event.c:5714
>  hci_le_enh_conn_complete_evt+0x23d/0x380 net/bluetooth/hci_event.c:5861
>  hci_le_meta_evt+0x357/0x5e0 net/bluetooth/hci_event.c:7408
>  hci_event_func net/bluetooth/hci_event.c:7716 [inline]
>  hci_event_packet+0x685/0x11c0 net/bluetooth/hci_event.c:7773
>  hci_rx_work+0x2c9/0xeb0 net/bluetooth/hci_core.c:4076
>  process_one_work+0x9ba/0x1b20 kernel/workqueue.c:3257
>  process_scheduled_works kernel/workqueue.c:3340 [inline]
>  worker_thread+0x6c8/0xf10 kernel/workqueue.c:3421
>  kthread+0x3c5/0x780 kernel/kthread.c:463
>  ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
>
> Freed by task 5932:
>  kasan_save_stack+0x33/0x60 mm/kasan/common.c:56
>  kasan_save_track+0x14/0x30 mm/kasan/common.c:77
>  __kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:587
>  kasan_save_free_info mm/kasan/kasan.h:406 [inline]
>  poison_slab_object mm/kasan/common.c:252 [inline]
>  __kasan_slab_free+0x5f/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:6663 [inline]
>  kfree+0x2f8/0x6e0 mm/slub.c:6871
>  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+0x1e7/0x590 lib/kobject.c:737
>  put_device drivers/base/core.c:3797 [inline]
>  device_unregister+0x2f/0xc0 drivers/base/core.c:3920
>  hci_conn_del_sysfs+0xb4/0x180 net/bluetooth/hci_sysfs.c:79
>  hci_conn_cleanup net/bluetooth/hci_conn.c:173 [inline]
>  hci_conn_del+0x657/0x1180 net/bluetooth/hci_conn.c:1234
>  hci_disconn_complete_evt+0x410/0xa00 net/bluetooth/hci_event.c:3451
>  hci_event_func net/bluetooth/hci_event.c:7719 [inline]
>  hci_event_packet+0xa10/0x11c0 net/bluetooth/hci_event.c:7773
>  hci_rx_work+0x2c9/0xeb0 net/bluetooth/hci_core.c:4076
>  process_one_work+0x9ba/0x1b20 kernel/workqueue.c:3257
>  process_scheduled_works kernel/workqueue.c:3340 [inline]
>  worker_thread+0x6c8/0xf10 kernel/workqueue.c:3421
>  kthread+0x3c5/0x780 kernel/kthread.c:463
>  ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
>
> The buggy address belongs to the object at ffff8880796b0000
>  which belongs to the cache kmalloc-8k of size 8192
> The buggy address is located 16 bytes inside of
>  freed 8192-byte region [ffff8880796b0000, ffff8880796b2000)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x796b0
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 00fff00000000040 ffff88813ff27280 0000000000000000 0000000000000001
> raw: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
> head: 00fff00000000040 ffff88813ff27280 0000000000000000 0000000000000001
> head: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
> head: 00fff00000000003 ffffea0001e5ac01 00000000ffffffff 00000000ffffffff
> head: ffffffffffffffff 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
> 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC),
> pid 5657, tgid 5657 (dhcpcd-run-hook), ts 79819636908, free_ts
> 79814310558
>  set_page_owner include/linux/page_owner.h:32 [inline]
>  post_alloc_hook+0x1af/0x220 mm/page_alloc.c:1845
>  prep_new_page mm/page_alloc.c:1853 [inline]
>  get_page_from_freelist+0xd0b/0x31a0 mm/page_alloc.c:3879
>  __alloc_frozen_pages_noprof+0x25f/0x2440 mm/page_alloc.c:5183
>  alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
>  alloc_slab_page mm/slub.c:3075 [inline]
>  allocate_slab mm/slub.c:3248 [inline]
>  new_slab+0x2c3/0x430 mm/slub.c:3302
>  ___slab_alloc+0xe18/0x1c90 mm/slub.c:4651
>  __slab_alloc.constprop.0+0x63/0x110 mm/slub.c:4774
>  __slab_alloc_node mm/slub.c:4850 [inline]
>  slab_alloc_node mm/slub.c:5246 [inline]
>  __kmalloc_cache_noprof+0x477/0x800 mm/slub.c:5766
>  kmalloc_noprof include/linux/slab.h:957 [inline]
>  kzalloc_noprof include/linux/slab.h:1094 [inline]
>  tomoyo_print_bprm security/tomoyo/audit.c:26 [inline]
>  tomoyo_init_log+0xc8a/0x2140 security/tomoyo/audit.c:264
>  tomoyo_supervisor+0x302/0x13b0 security/tomoyo/common.c:2198
>  tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline]
>  tomoyo_env_perm+0x191/0x200 security/tomoyo/environ.c:63
>  tomoyo_environ security/tomoyo/domain.c:672 [inline]
>  tomoyo_find_next_domain+0xec1/0x20b0 security/tomoyo/domain.c:888
>  tomoyo_bprm_check_security security/tomoyo/tomoyo.c:102 [inline]
>  tomoyo_bprm_check_security+0x12d/0x1d0 security/tomoyo/tomoyo.c:92
>  security_bprm_check+0x1b9/0x1e0 security/security.c:794
>  search_binary_handler fs/exec.c:1659 [inline]
>  exec_binprm fs/exec.c:1701 [inline]
>  bprm_execve fs/exec.c:1753 [inline]
>  bprm_execve+0x81e/0x1620 fs/exec.c:1729
>  do_execveat_common.isra.0+0x4a5/0x610 fs/exec.c:1859
> page last free pid 5657 tgid 5657 stack trace:
>  reset_page_owner include/linux/page_owner.h:25 [inline]
>  free_pages_prepare mm/page_alloc.c:1394 [inline]
>  __free_frozen_pages+0x7df/0x1160 mm/page_alloc.c:2901
>  discard_slab mm/slub.c:3346 [inline]
>  __put_partials+0x130/0x170 mm/slub.c:3886
>  qlink_free mm/kasan/quarantine.c:163 [inline]
>  qlist_free_all+0x4c/0xf0 mm/kasan/quarantine.c:179
>  kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
>  __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:352
>  kasan_slab_alloc include/linux/kasan.h:252 [inline]
>  slab_post_alloc_hook mm/slub.c:4948 [inline]
>  slab_alloc_node mm/slub.c:5258 [inline]
>  __kmalloc_cache_noprof+0x274/0x800 mm/slub.c:5766
>  kmalloc_noprof include/linux/slab.h:957 [inline]
>  tomoyo_print_header security/tomoyo/audit.c:156 [inline]
>  tomoyo_init_log+0x197/0x2140 security/tomoyo/audit.c:255
>  tomoyo_supervisor+0x302/0x13b0 security/tomoyo/common.c:2198
>  tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline]
>  tomoyo_env_perm+0x191/0x200 security/tomoyo/environ.c:63
>  tomoyo_environ security/tomoyo/domain.c:672 [inline]
>  tomoyo_find_next_domain+0xec1/0x20b0 security/tomoyo/domain.c:888
>  tomoyo_bprm_check_security security/tomoyo/tomoyo.c:102 [inline]
>  tomoyo_bprm_check_security+0x12d/0x1d0 security/tomoyo/tomoyo.c:92
>  security_bprm_check+0x1b9/0x1e0 security/security.c:794
>  search_binary_handler fs/exec.c:1659 [inline]
>  exec_binprm fs/exec.c:1701 [inline]
>  bprm_execve fs/exec.c:1753 [inline]
>  bprm_execve+0x81e/0x1620 fs/exec.c:1729
>  do_execveat_common.isra.0+0x4a5/0x610 fs/exec.c:1859
>  do_execve fs/exec.c:1933 [inline]
>  __do_sys_execve fs/exec.c:2009 [inline]
>  __se_sys_execve fs/exec.c:2004 [inline]
>  __x64_sys_execve+0x8e/0xb0 fs/exec.c:2004
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
>
> Memory state around the buggy address:
>  ffff8880796aff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8880796aff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff8880796b0000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                          ^
>  ffff8880796b0080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880796b0100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> Fixes: a106e50be74b ("Bluetooth: HCI: Add support for LL Extended Feature Set")
> Reported-by: syzbot+87badbb9094e008e0685@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzbot.org/bug?extid=87badbb9094e008e0685
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
> ---
>  net/bluetooth/hci_sync.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index 45d16639874a..f67a32c1451e 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -7371,7 +7371,7 @@ static void le_read_features_complete(struct
> hci_dev *hdev, void *data, int err)
>         if (err == -ECANCELED)
>                 return;
>
> -       hci_conn_drop(conn);
> +       hci_conn_put(conn);
>  }
>
>  static int hci_le_read_all_remote_features_sync(struct hci_dev *hdev,
> @@ -7441,7 +7441,7 @@ int hci_le_read_remote_features(struct hci_conn *conn)
>         if (conn->out || (hdev->le_features[0] & HCI_LE_PERIPHERAL_FEATURES))
>                 err = hci_cmd_sync_queue_once(hdev,
>                                               hci_le_read_remote_features_sync,
> -                                             hci_conn_hold(conn),
> +                                             hci_conn_get(conn),
>                                               le_read_features_complete);
>         else
>                 err = -EOPNOTSUPP;
> --
> 2.53.0
>
>
>
> --
> Luiz Augusto von Dentz



-- 
Luiz Augusto von Dentz