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References: <20201105002412.37720-1-sonnysasaka@chromium.org>
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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Thu, 5 Nov 2020 10:46:25 -0800
Message-ID: <CABBYNZ+=wukeRdRD9p=46NAeHhmSVSkAieJCya2UvMz-=zf3sg@mail.gmail.com>
Subject: Re: [PATCH BlueZ] gatt-client: Do not continue service discovery if disconnected
To:     Sonny Sasaka <sonnysasaka@chromium.org>
Cc:     "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>,
        Archie Pusaka <apusaka@chromium.org>
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Hi Sonny,

On Wed, Nov 4, 2020 at 10:01 PM Sonny Sasaka <sonnysasaka@chromium.org> wrote:
>
> If device is disconnected, discovery_complete_op should not continue
> processing since this can lead to a crash because the GATT-related
> objects may already be freed.
>
> Sample crash stack trace:
> 0  gatt_db_service_get_handles (service=0x1751130, service=0x1751130, end_handle=0x7ffcd600806e, start_handle=0x7ffcd600806c) at src/shared/gatt-db.c:569
> 1  gatt_db_attribute_get_service_data (attrib=<optimized out>, start_handle=0x7ffcd600806c, end_handle=0x7ffcd600806e, primary=0x0, uuid=0x0) at src/shared/gatt-db.c:1657
> 2  0x00000000004983a8 in discovery_op_complete (op=op@entry=0x173b320, success=<optimized out>, err=err@entry=10 '\n') at src/shared/gatt-client.c:406
> 3  0x000000000049a548 in discover_descs_cb (success=<optimized out>, att_ecode=<optimized out>, result=<optimized out>, user_data=0x173b320) at src/shared/gatt-client.c:915
> 4  0x00000000004a1d87 in discovery_op_complete (op=0x1748450, success=<optimized out>, ecode=<optimized out>) at src/shared/gatt-helpers.c:615
> 5  0x00000000004a2379 in discover_descs_cb (opcode=<optimized out>, pdu=0x174d551, length=<optimized out>, user_data=0x1748450) at src/shared/gatt-helpers.c:1465
> 6  0x00000000004966db in handle_rsp (pdu_len=4, pdu=<optimized out>, opcode=<optimized out>, chan=0x17483c0) at src/shared/att.c:814
> 7  can_read_data (io=<optimized out>, user_data=0x17483c0) at src/shared/att.c:1011

Weird, are you still receiving data after the device is disconnected?

> 8  0x00000000004a0853 in watch_callback (channel=<optimized out>, cond=<optimized out>, user_data=<optimized out>) at src/shared/io-glib.c:157
> 9  0x00007fb3f2d7fe87 in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
> 10 0x00007fb3f2d80230 in ?? () from /usr/lib64/libglib-2.0.so.0
> 11 0x00007fb3f2d80542 in g_main_loop_run () from /usr/lib64/libglib-2.0.so.0
> 12 0x00000000004a0e25 in mainloop_run () at src/shared/mainloop-glib.c:66
> 13 0x00000000004a11f2 in mainloop_run_with_signal (func=func@entry=0x43f200 <signal_callback>, user_data=user_data@entry=0x0) at src/shared/mainloop-notify.c:188
> 14 0x000000000040c72e in main (argc=<optimized out>, argv=<optimized out>) at src/main.c:959
>
> Reviewed-By: Archie Pusaka <apusaka@chromium.org>
>
> ---
>  src/device.c             |  3 +++
>  src/shared/gatt-client.c | 20 ++++++++++++++++++++
>  src/shared/gatt-client.h |  2 ++
>  3 files changed, 25 insertions(+)
>
> diff --git a/src/device.c b/src/device.c
> index a5ef46730..9dad746eb 100644
> --- a/src/device.c
> +++ b/src/device.c
> @@ -586,6 +586,9 @@ static void gatt_client_cleanup(struct btd_device *device)
>                 device->gatt_ready_id = 0;
>         }
>
> +       /* Make sure that service discovery is stopped if any is in progress */
> +       bt_gatt_client_reset_in_discovery(device->client);

Does this means that other references will also get interrupted? That
is something very weird here since when disconnected the bt_att
instance should actually have informed the bt_gatt_client and the
cleanup should had happened there.

> +
>         bt_gatt_client_unref(device->client);
>         device->client = NULL;
>  }
> diff --git a/src/shared/gatt-client.c b/src/shared/gatt-client.c
> index 8becf1c6c..2ba6efe9a 100644
> --- a/src/shared/gatt-client.c
> +++ b/src/shared/gatt-client.c
> @@ -104,6 +104,9 @@ struct bt_gatt_client {
>
>         struct bt_gatt_request *discovery_req;
>         unsigned int mtu_req_id;
> +
> +       /* Whether there is a service discovery operation ongoing */
> +       bool in_discovery;
>  };
>
>  struct request {
> @@ -381,6 +384,12 @@ static void discovery_op_complete(struct discovery_op *op, bool success,
>  {
>         const struct queue_entry *svc;
>
> +       /* Service discovery may be reset due to disconnection */
> +       if (!op->client->in_discovery)
> +               return;
> +
> +       op->client->in_discovery = false;
> +
>         op->success = success;
>
>         /* Read database hash if discovery has been successful */
> @@ -1857,6 +1866,9 @@ static void process_service_changed(struct bt_gatt_client *client,
>  {
>         struct discovery_op *op;
>
> +       if (client->in_discovery)
> +               goto fail;
> +
>         op = discovery_op_create(client, start_handle, end_handle,
>                                                 service_changed_complete,
>                                                 service_changed_failure);
> @@ -1869,6 +1881,7 @@ static void process_service_changed(struct bt_gatt_client *client,
>                                                 discovery_op_ref(op),
>                                                 discovery_op_unref);
>         if (client->discovery_req) {
> +               client->in_discovery = true;
>                 client->in_svc_chngd = true;
>                 return;
>         }
> @@ -2057,6 +2070,7 @@ static bool gatt_client_init(struct bt_gatt_client *client, uint16_t mtu)
>                 return false;
>         }
>
> +       client->in_discovery = true;
>         client->in_init = true;
>
>         return true;
> @@ -2080,6 +2094,7 @@ discover:
>         }
>
>  done:
> +       client->in_discovery = true;
>         client->in_init = true;
>         return true;
>  }
> @@ -3694,3 +3709,8 @@ int bt_gatt_client_get_security(struct bt_gatt_client *client)
>
>         return bt_att_get_security(client->att, NULL);
>  }
> +
> +void bt_gatt_client_reset_in_discovery(struct bt_gatt_client *client)
> +{
> +       client->in_discovery = false;
> +}
> diff --git a/src/shared/gatt-client.h b/src/shared/gatt-client.h
> index dc5102394..dcd8e5cf6 100644
> --- a/src/shared/gatt-client.h
> +++ b/src/shared/gatt-client.h
> @@ -126,3 +126,5 @@ bool bt_gatt_client_unregister_notify(struct bt_gatt_client *client,
>
>  bool bt_gatt_client_set_security(struct bt_gatt_client *client, int level);
>  int bt_gatt_client_get_security(struct bt_gatt_client *client);
> +
> +void bt_gatt_client_reset_in_discovery(struct bt_gatt_client *client);
> --
> 2.26.2
>


-- 
Luiz Augusto von Dentz