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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Fri, 22 Jul 2022 13:06:39 -0700
Message-ID: <CABBYNZ+k+ZOVNi+GYgdiK+B+tqKQXTWYp1QG4JSE_7EwZHNBMw@mail.gmail.com>
Subject: Re: [PATCH] Bluetooth: hci_sync: Use safe loop when adding accept list
To:     Archie Pusaka <apusaka@google.com>
Cc:     linux-bluetooth <linux-bluetooth@vger.kernel.org>,
        Marcel Holtmann <marcel@holtmann.org>,
        CrosBT Upstreaming <chromeos-bluetooth-upstreaming@chromium.org>,
        Archie Pusaka <apusaka@chromium.org>,
        Zhengping Jiang <jiangzp@google.com>,
        Michael Sun <michaelfsun@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>
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Hi Archie,

On Fri, Jul 22, 2022 at 3:23 AM Archie Pusaka <apusaka@google.com> wrote:
>
> From: Archie Pusaka <apusaka@chromium.org>
>
> When in the middle of adding accept list, the userspace can still
> remove devices, therefore causing crash if the removed device is
> the one being processed.
>
> Use a safe loop mechanism to guard against deletion while iterating
> the pending items.
>
> Below is a sample btsnoop log when user enters wrong passkey when
> pairing a LE keyboard and the corresponding stacktrace.
> @ MGMT Event: Command Complete (0x0001) plen 10
>       Add Device (0x0033) plen 7
>         Status: Success (0x00)
>         LE Address: CA:CA:BD:78:37:F9 (Static)
> < HCI Command: LE Add Device To Accept List (0x08|0x0011) plen 7
>         Address type: Random (0x01)
>         Address: CA:CA:BD:78:37:F9 (Static)
> @ MGMT Event: Device Removed (0x001b) plen 7
>         LE Address: CA:CA:BD:78:37:F9 (Static)
> > HCI Event: Command Complete (0x0e) plen 4
>       LE Add Device To Accept List (0x08|0x0011) ncmd 1
>         Status: Success (0x00)
>
> [  167.409813] Call trace:
> [  167.409983]  hci_le_add_accept_list_sync+0x64/0x26c
> [  167.410150]  hci_update_passive_scan_sync+0x5f0/0x6dc
> [  167.410318]  add_device_sync+0x18/0x24
> [  167.410486]  hci_cmd_sync_work+0xe8/0x150
> [  167.410509]  process_one_work+0x140/0x4d0
> [  167.410526]  worker_thread+0x134/0x2e4
> [  167.410544]  kthread+0x148/0x160
> [  167.410562]  ret_from_fork+0x10/0x30
>
> Signed-off-by: Archie Pusaka <apusaka@chromium.org>
> Reviewed-by: Zhengping Jiang <jiangzp@google.com>
> Reviewed-by: Michael Sun <michaelfsun@google.com>
>
> ---
>
>  net/bluetooth/hci_sync.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index 3067d94e7a8e..8e843d34f7de 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -1863,7 +1863,7 @@ struct sk_buff *hci_read_local_oob_data_sync(struct hci_dev *hdev,
>   */
>  static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
>  {
> -       struct hci_conn_params *params;
> +       struct hci_conn_params *params, *tmp;
>         struct bdaddr_list *b, *t;
>         u8 num_entries = 0;
>         bool pend_conn, pend_report;
> @@ -1930,7 +1930,7 @@ static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
>          * just abort and return filer policy value to not use the
>          * accept list.
>          */
> -       list_for_each_entry(params, &hdev->pend_le_conns, action) {
> +       list_for_each_entry_safe(params, tmp, &hdev->pend_le_conns, action) {
>                 err = hci_le_add_accept_list_sync(hdev, params, &num_entries);
>                 if (err)
>                         goto done;
> @@ -1940,7 +1940,7 @@ static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
>          * the list of pending reports and also add these to the
>          * accept list if there is still space. Abort if space runs out.
>          */
> -       list_for_each_entry(params, &hdev->pend_le_reports, action) {
> +       list_for_each_entry_safe(params, tmp, &hdev->pend_le_reports, action) {
>                 err = hci_le_add_accept_list_sync(hdev, params, &num_entries);
>                 if (err)
>                         goto done;

Hmm if this happens it means other threads are actually interfering
with cmd_sync queue which is something that is probably a bug since
the whole point of cmd_sync is to serialize the commands making it
easier to do more complex state updates (such accept+resolve list
updates), we could perhaps still apply this change as a workaround but
ultimately I think it would be better to add a mgmt-tester reproducing
the issue and have a proper fix of the code updating the list from a
different thread.

> --
> 2.37.1.359.gd136c6c3e2-goog
>


-- 
Luiz Augusto von Dentz