Hi Dagan,
On Thu, Sep 30, 2021 at 8:24 AM Dagan Martinez <dmartinez@xxxxxxxxxx> wrote:
>
> Allow a GATT server to impose permissions/restrictions on a CCC by
> setting additional `X-notify` and `X-indicate` permissions on its
> associated characteristic.
>
> This allows a developer to require encryption/authentication in order
> for a GATT client to subscribe to server-initiated updates.
>
> Test procedure:
> Attempt to read/write with a "low" security level on an unprotected CCC
> using gatttool, and succeed
> Attempt to READ with a "low" security level on an protected CCC
> using gatttool, and succeed
> Attempt to WRITE with a "low" security level on an protected CCC
> using gatttool, and fail
> Attempt to read/write while paired on a protected CCC using
> `bluetoothctl`, and succeed
> ---
> src/gatt-database.c | 42 ++++++++++++++++++++++++++++++++++++++----
> src/shared/att-types.h | 4 ++++
> 2 files changed, 42 insertions(+), 4 deletions(-)
>
> diff --git a/src/gatt-database.c b/src/gatt-database.c
> index 68f411ba4..fd4a39166 100644
> --- a/src/gatt-database.c
> +++ b/src/gatt-database.c
> @@ -1060,17 +1060,33 @@ service_add_ccc(struct gatt_db_attribute *service,
> struct btd_gatt_database *database,
> btd_gatt_database_ccc_write_t write_callback,
> void *user_data,
> + uint32_t parent_permissions,
> btd_gatt_database_destroy_t destroy)
> {
> struct gatt_db_attribute *ccc;
> struct ccc_cb_data *ccc_cb;
> bt_uuid_t uuid;
> + uint32_t permissions;
>
> ccc_cb = new0(struct ccc_cb_data, 1);
>
> + /*
> + * Provide a way for the permissions on a characteristic to dictate
> + * the permissions on the CCC
> + */
> + permissions = BT_ATT_PERM_READ | BT_ATT_PERM_WRITE;
> +
> + if (parent_permissions & BT_ATT_PERM_SERVER_INITIATED_UPDATE_ENCRYPT)
> + permissions |= BT_ATT_PERM_WRITE_ENCRYPT;
> +
> + if (parent_permissions & BT_ATT_PERM_SERVER_INITIATED_UPDATE_AUTHEN)
> + permissions |= BT_ATT_PERM_WRITE_AUTHEN;
> +
> + if (parent_permissions & BT_ATT_PERM_SERVER_INITIATED_UPDATE_SECURE)
> + permissions |= BT_ATT_PERM_WRITE_SECURE;
> +
> bt_uuid16_create(&uuid, GATT_CLIENT_CHARAC_CFG_UUID);
> - ccc = gatt_db_service_add_descriptor(service, &uuid,
> - BT_ATT_PERM_READ | BT_ATT_PERM_WRITE,
> + ccc = gatt_db_service_add_descriptor(service, &uuid, permissions,
> gatt_ccc_read_cb, gatt_ccc_write_cb, database);
> if (!ccc) {
> error("Failed to create CCC entry in database");
> @@ -1227,7 +1243,7 @@ static void populate_gatt_service(struct btd_gatt_database *database)
> NULL, NULL, database);
>
> database->svc_chngd_ccc = service_add_ccc(service, database, NULL, NULL,
> - NULL);
> + 0, NULL);
>
> bt_uuid16_create(&uuid, GATT_CHARAC_CLI_FEAT);
> database->cli_feat = gatt_db_service_add_characteristic(service,
> @@ -1690,6 +1706,24 @@ static bool parse_chrc_flags(DBusMessageIter *array, uint8_t *props,
> *perm |= BT_ATT_PERM_WRITE | BT_ATT_PERM_WRITE_SECURE;
> } else if (!strcmp("authorize", flag)) {
> *req_prep_authorization = true;
> + } else if (!strcmp("encrypt-notify", flag)) {
> + *perm |= BT_ATT_PERM_SERVER_INITIATED_UPDATE_ENCRYPT;
> + *props |= BT_GATT_CHRC_PROP_NOTIFY;
> + } else if (!strcmp("encrypt-authenticated-notify", flag)) {
> + *perm |= BT_ATT_PERM_SERVER_INITIATED_UPDATE_AUTHEN;
> + *props |= BT_GATT_CHRC_PROP_NOTIFY;
> + } else if (!strcmp("secure-notify", flag)) {
> + *perm |= BT_ATT_PERM_SERVER_INITIATED_UPDATE_SECURE;
> + *props |= BT_GATT_CHRC_PROP_NOTIFY;
> + } else if (!strcmp("encrypt-indicate", flag)) {
> + *perm |= BT_ATT_PERM_SERVER_INITIATED_UPDATE_ENCRYPT;
> + *props |= BT_GATT_CHRC_PROP_INDICATE;
> + } else if (!strcmp("encrypt-authenticated-indicate", flag)) {
> + *perm |= BT_ATT_PERM_SERVER_INITIATED_UPDATE_AUTHEN;
> + *props |= BT_GATT_CHRC_PROP_INDICATE;
> + } else if (!strcmp("secure-indicate", flag)) {
> + *perm |= BT_ATT_PERM_SERVER_INITIATED_UPDATE_SECURE;
> + *props |= BT_GATT_CHRC_PROP_INDICATE;
> } else {
> error("Invalid characteristic flag: %s", flag);
> return false;
> @@ -2796,7 +2830,7 @@ static bool database_add_ccc(struct external_service *service,
> return true;
>
> chrc->ccc = service_add_ccc(service->attrib, service->app->database,
> - ccc_write_cb, chrc, NULL);
> + ccc_write_cb, chrc, chrc->perm, NULL);
> if (!chrc->ccc) {
> error("Failed to create CCC entry for characteristic");
> return false;
> diff --git a/src/shared/att-types.h b/src/shared/att-types.h
> index a08b24155..eb5def503 100644
> --- a/src/shared/att-types.h
> +++ b/src/shared/att-types.h
> @@ -137,6 +137,10 @@ struct bt_att_pdu_error_rsp {
> BT_ATT_PERM_WRITE_AUTHEN | \
> BT_ATT_PERM_WRITE_ENCRYPT | \
> BT_ATT_PERM_WRITE_SECURE)
> +/* Permissions to be applied to the CCC*/
> +#define BT_ATT_PERM_SERVER_INITIATED_UPDATE_ENCRYPT 0x0400
> +#define BT_ATT_PERM_SERVER_INITIATED_UPDATE_AUTHEN 0x0800
> +#define BT_ATT_PERM_SERVER_INITIATED_UPDATE_SECURE 0x1000
I don't think we really need these above, how about we do something
like the following:
https://gist.github.com/Vudentz/af6899625df3d83b62cfbc61bbd4b94b
That way we don't need to define more permissions since we can just
reuse the existing one which imo are easier to understand.
> /* GATT Characteristic Properties Bitfield values */
> #define BT_GATT_CHRC_PROP_BROADCAST 0x01
> --
> 2.31.1
Btw, it would be great to have an example using the new flags in the
patch description, bluetoothctl> register-characteristic...
--
Luiz Augusto von Dentz
