Re: [PATCH] advertising: Fix crash when advertisement is unregistered while MGMT ADD_ADVERTISEMENT call

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

Hi Simon,

On Thu, Oct 31, 2019 at 9:45 AM Simon Mikuda
<simon.mikuda@streamunlimited.com> wrote:

Subject should be less than 72 characters so it first nicely on git
shortlog, you can add a short description before the backtrace.

> bluetoothd[29698]: src/advertising.c:register_advertisement() RegisterAdvertisement
> bluetoothd[29698]: src/advertising.c:client_create() Adding proxy for /org/bluez/example/advertisement0
> bluetoothd[29698]: src/advertising.c:register_advertisement() Registered advertisement at path /org/bluez/example/advertisement0
> bluetoothd[29698]: src/advertising.c:parse_service_uuids() Adding ServiceUUID: 180D
> bluetoothd[29698]: src/advertising.c:parse_service_uuids() Adding ServiceUUID: 180F
> bluetoothd[29698]: src/advertising.c:parse_manufacturer_data() Adding ManufacturerData for ffff
> bluetoothd[29698]: src/advertising.c:parse_service_data() Adding ServiceData for 9999
> bluetoothd[29698]: src/advertising.c:parse_data() Adding Data for type 0x26 len 3
> bluetoothd[29698]: src/advertising.c:refresh_adv() Refreshing advertisement: /org/bluez/example/advertisement0
> bluetoothd[29698]: src/advertising.c:unregister_advertisement() UnregisterAdvertisement
> bluetoothd[29698]: src/advertising.c:add_adv_callback() Advertisement registered: �
> Segmentation fault (core dumped)
> ---
>  src/advertising.c | 53 +++++++++++++++++++++++++++++------------------------
>  1 file changed, 29 insertions(+), 24 deletions(-)
>
> diff --git a/src/advertising.c b/src/advertising.c
> index 3ed1376..7d8cadf 100644
> --- a/src/advertising.c
> +++ b/src/advertising.c
> @@ -63,6 +63,8 @@ struct btd_adv_manager {
>  #define AD_TYPE_PERIPHERAL 1
>
>  struct btd_adv_client {
> +       int ref_count;
> +
>         struct btd_adv_manager *manager;
>         char *owner;
>         char *path;
> @@ -136,13 +138,6 @@ static void client_free(void *data)
>         free(client);
>  }
>
> -static gboolean client_free_idle_cb(void *data)
> -{
> -       client_free(data);
> -
> -       return FALSE;
> -}
> -
>  static void client_release(void *data)
>  {
>         struct btd_adv_client *client = data;
> @@ -175,12 +170,19 @@ static void remove_advertising(struct btd_adv_manager *manager,
>                         manager->mgmt_index, sizeof(cp), &cp, NULL, NULL, NULL);
>  }
>
> -static void client_remove(void *data)
> +static struct btd_adv_client *client_ref(struct btd_adv_client *client)
> +{
> +       __sync_fetch_and_add(&client->ref_count, 1);
> +
> +       return client;
> +}
> +
> +static void client_unref(struct btd_adv_client *client)
>  {
> -       struct btd_adv_client *client = data;
>         struct mgmt_cp_remove_advertising cp;
>
> -       g_dbus_client_set_disconnect_watch(client->client, NULL, NULL);
> +       if (__sync_sub_and_fetch(&client->ref_count, 1))
> +               return;

While the idea of using refcount to protect might seem good I think we
would be better off using mgmt_cancel for this case so the callback is
not called, or you are not using it on purpose?

>         cp.instance = client->instance;
>
> @@ -188,10 +190,6 @@ static void client_remove(void *data)
>                         client->manager->mgmt_index, sizeof(cp), &cp,
>                         NULL, NULL, NULL);
>
> -       queue_remove(client->manager->clients, client);
> -
> -       g_idle_add(client_free_idle_cb, client);
> -
>         g_dbus_emit_property_changed(btd_get_dbus_connection(),
>                                 adapter_get_path(client->manager->adapter),
>                                 LE_ADVERTISING_MGR_IFACE, "SupportedInstances");
> @@ -199,13 +197,18 @@ static void client_remove(void *data)
>         g_dbus_emit_property_changed(btd_get_dbus_connection(),
>                                 adapter_get_path(client->manager->adapter),
>                                 LE_ADVERTISING_MGR_IFACE, "ActiveInstances");
> +
> +       queue_remove(client->manager->clients, client);
> +
> +       client_free(client);
> +
>  }
>
>  static void client_disconnect_cb(DBusConnection *conn, void *user_data)
>  {
>         DBG("Client disconnected");
>
> -       client_remove(user_data);
> +       client_unref(user_data);
>  }
>
>  static bool parse_type(DBusMessageIter *iter, struct btd_adv_client *client)
> @@ -564,7 +567,7 @@ static gboolean client_timeout(void *user_data)
>         client->to_id = 0;
>
>         client_release(client);
> -       client_remove(client);
> +       client_unref(client);
>
>         return FALSE;
>  }
> @@ -963,8 +966,6 @@ static void add_client_complete(struct btd_adv_client *client, uint8_t status)
>                                                 mgmt_errstr(status), status);
>                 reply = btd_error_failed(client->reg,
>                                         "Failed to register advertisement");
> -               queue_remove(client->manager->clients, client);
> -               g_idle_add(client_free_idle_cb, client);
>
>         } else
>                 reply = dbus_message_new_method_return(client->reg);
> @@ -972,6 +973,8 @@ static void add_client_complete(struct btd_adv_client *client, uint8_t status)
>         g_dbus_send_message(btd_get_dbus_connection(), reply);
>         dbus_message_unref(client->reg);
>         client->reg = NULL;
> +
> +       client_unref(client);
>  }
>
>  static void add_adv_callback(uint8_t status, uint16_t length,
> @@ -1060,8 +1063,11 @@ static DBusMessage *parse_advertisement(struct btd_adv_client *client)
>         }
>
>         err = refresh_adv(client, add_adv_callback);
> -       if (!err)
> +       if (!err) {
> +               /* Hold reference to client until add_adv_callback is finished */
> +               client_ref(client);
>                 return NULL;
> +       }
>
>  fail:
>         return btd_error_failed(client->reg, "Failed to parse advertisement.");
> @@ -1082,14 +1088,12 @@ static void client_proxy_added(GDBusProxy *proxy, void *data)
>                 return;
>
>         /* Failed to publish for some reason, remove. */
> -       queue_remove(client->manager->clients, client);
> -
> -       g_idle_add(client_free_idle_cb, client);
> -
>         g_dbus_send_message(btd_get_dbus_connection(), reply);
>
>         dbus_message_unref(client->reg);
>         client->reg = NULL;
> +
> +       client_unref(client);
>  }
>
>  static struct btd_adv_client *client_create(struct btd_adv_manager *manager,
> @@ -1189,6 +1193,7 @@ static DBusMessage *register_advertisement(DBusConnection *conn,
>         DBG("Registered advertisement at path %s", match.path);
>
>         queue_push_tail(manager->clients, client);
> +       client_ref(client);
>
>         return NULL;
>  }
> @@ -1218,7 +1223,7 @@ static DBusMessage *unregister_advertisement(DBusConnection *conn,
>         if (!client)
>                 return btd_error_does_not_exist(msg);
>
> -       client_remove(client);
> +       client_unref(client);
>
>         return dbus_message_new_method_return(msg);
>  }
> --
> 2.7.4
>


-- 
Luiz Augusto von Dentz