Re: [PATCH BlueZ v3 1/2] gatt: Allow GATT server to dicate CCC permissions

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