Re: [PATCH BlueZ] gatt-client: Do not continue service discovery if disconnected

[Sonny Sasaka <sonnysasaka@chromium.org>]

Hi Luiz,


On Thu, Nov 5, 2020 at 10:46 AM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> 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?
To be more precise, this happens if I do "remove device" from
bluetoothctl while it's still doing GATT discovery, i.e. connect and
quickly remove device. Also this is reproducible if the GATT.Cache
config is set to "yes". So, the "disconnection" may not be physical
but a consequence of the code path of the RemoveDevice API. I can
reproduce it almost 100% of the time with an LE Mouse (tried with MS
Mouse 3600 and Logitech M355).
>
> > 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.
What do you mean by "other references"? My guess is that
bt_gatt_client has done the cleanup, but discovery_op_complete still
tries to execute the whole code path which involves accessing the
already cleaned-up gatt_db_attribute objects.
>
> > +
> >         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