Re: [syzbot] Re: [PATCH v1] Bluetooth: MGMT: Use RCU-protected in mgmt_pending list

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Subject: Re: [PATCH v1] Bluetooth: MGMT: Use RCU-protected in mgmt_pending list
Author: luiz.dentz@gmail.com

#syz test

On Wed, May 28, 2025 at 2:44 PM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
>
> This uses RCU procedures to protect from concurrent access of
> mgmt_pending list which can cause crashes like:
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in mgmt_remove_adv_monitor_complete+0xe5/0x540 net/bluetooth/mgmt.c:5405
> Read of size 8 at addr ffff888048891a18 by task kworker/u5:8/5333
>
> CPU: 0 UID: 0 PID: 5333 Comm: kworker/u5:8 Not tainted 6.15.0-rc5-syzkaller-00197-gea34704d6ad7 #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Workqueue: hci0 hci_cmd_sync_work
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  print_address_description mm/kasan/report.c:408 [inline]
>  print_report+0xb4/0x290 mm/kasan/report.c:521
>  kasan_report+0x118/0x150 mm/kasan/report.c:634
>  mgmt_remove_adv_monitor_complete+0xe5/0x540 net/bluetooth/mgmt.c:5405
>  hci_cmd_sync_work+0x25e/0x3a0 net/bluetooth/hci_sync.c:334
>  process_one_work kernel/workqueue.c:3238 [inline]
>  process_scheduled_works+0xadb/0x17a0 kernel/workqueue.c:3319
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
>  kthread+0x70e/0x8a0 kernel/kthread.c:464
>  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
>
> Allocated by task 5702:
>  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:377 [inline]
>  __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394
>  kasan_kmalloc include/linux/kasan.h:260 [inline]
>  __kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4358
>  kmalloc_noprof include/linux/slab.h:905 [inline]
>  kzalloc_noprof include/linux/slab.h:1039 [inline]
>  mgmt_pending_new+0x65/0x240 net/bluetooth/mgmt_util.c:252
>  mgmt_pending_add+0x34/0x120 net/bluetooth/mgmt_util.c:279
>  remove_adv_monitor+0x103/0x1b0 net/bluetooth/mgmt.c:5453
>  hci_mgmt_cmd+0x9c6/0xef0 net/bluetooth/hci_sock.c:1712
>  hci_sock_sendmsg+0x6ca/0xee0 net/bluetooth/hci_sock.c:1832
>  sock_sendmsg_nosec net/socket.c:712 [inline]
>  __sock_sendmsg+0x219/0x270 net/socket.c:727
>  sock_write_iter+0x258/0x330 net/socket.c:1131
>  new_sync_write fs/read_write.c:591 [inline]
>  vfs_write+0x548/0xa90 fs/read_write.c:684
>  ksys_write+0x145/0x250 fs/read_write.c:736
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Freed by task 5700:
>  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:247 [inline]
>  __kasan_slab_free+0x62/0x70 mm/kasan/common.c:264
>  kasan_slab_free include/linux/kasan.h:233 [inline]
>  slab_free_hook mm/slub.c:2380 [inline]
>  slab_free mm/slub.c:4642 [inline]
>  kfree+0x193/0x440 mm/slub.c:4841
>  mgmt_pending_foreach+0xc9/0x120 net/bluetooth/mgmt_util.c:242
>  mgmt_index_removed+0x10d/0x2f0 net/bluetooth/mgmt.c:9362
>  hci_sock_bind+0xbe9/0x1000 net/bluetooth/hci_sock.c:1307
>  __sys_bind_socket net/socket.c:1810 [inline]
>  __sys_bind+0x2c3/0x3e0 net/socket.c:1841
>  __do_sys_bind net/socket.c:1846 [inline]
>  __se_sys_bind net/socket.c:1844 [inline]
>  __x64_sys_bind+0x7a/0x90 net/socket.c:1844
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Fixes: a380b6cff1a2 ("Bluetooth: Add generic mgmt helper API")
> Closes: https://syzkaller.appspot.com/bug?extid=feb0dc579bbe30a13190
> Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> ---
>  net/bluetooth/mgmt_util.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/net/bluetooth/mgmt_util.c b/net/bluetooth/mgmt_util.c
> index 3713ff490c65..c2dc8ddf5f78 100644
> --- a/net/bluetooth/mgmt_util.c
> +++ b/net/bluetooth/mgmt_util.c
> @@ -219,13 +219,20 @@ struct mgmt_pending_cmd *mgmt_pending_find(unsigned short channel, u16 opcode,
>  {
>         struct mgmt_pending_cmd *cmd;
>
> -       list_for_each_entry(cmd, &hdev->mgmt_pending, list) {
> +       rcu_read_lock();
> +
> +       list_for_each_entry_rcu(cmd, &hdev->mgmt_pending, list) {
>                 if (hci_sock_get_channel(cmd->sk) != channel)
>                         continue;
> -               if (cmd->opcode == opcode)
> +
> +               if (cmd->opcode == opcode) {
> +                       rcu_read_unlock();
>                         return cmd;
> +               }
>         }
>
> +       rcu_read_unlock();
> +
>         return NULL;
>  }
>
> @@ -233,14 +240,11 @@ void mgmt_pending_foreach(u16 opcode, struct hci_dev *hdev,
>                           void (*cb)(struct mgmt_pending_cmd *cmd, void *data),
>                           void *data)
>  {
> -       struct mgmt_pending_cmd *cmd, *tmp;
> -
> -       list_for_each_entry_safe(cmd, tmp, &hdev->mgmt_pending, list) {
> -               if (opcode > 0 && cmd->opcode != opcode)
> -                       continue;
> +       struct mgmt_pending_cmd *cmd;
>
> +       cmd = mgmt_pending_find(HCI_CHANNEL_CONTROL, opcode, hdev);
> +       if (cmd)
>                 cb(cmd, data);
> -       }
>  }
>
>  struct mgmt_pending_cmd *mgmt_pending_new(struct sock *sk, u16 opcode,
> @@ -280,7 +284,7 @@ struct mgmt_pending_cmd *mgmt_pending_add(struct sock *sk, u16 opcode,
>         if (!cmd)
>                 return NULL;
>
> -       list_add_tail(&cmd->list, &hdev->mgmt_pending);
> +       list_add_tail_rcu(&cmd->list, &hdev->mgmt_pending);
>
>         return cmd;
>  }
> @@ -294,7 +298,8 @@ void mgmt_pending_free(struct mgmt_pending_cmd *cmd)
>
>  void mgmt_pending_remove(struct mgmt_pending_cmd *cmd)
>  {
> -       list_del(&cmd->list);
> +       list_del_rcu(&cmd->list);
> +       synchronize_rcu();
>         mgmt_pending_free(cmd);
>  }
>
> --
> 2.49.0
>


--
Luiz Augusto von Dentz