Allow a GATT server to impose write permissions/restrictions on a CCC by
setting additional `X-notify` and `X-indicate` flags on its associated
characteristic.
This allows a developer to require encryption/authentication in order
for a GATT client to subscribe to server-initiated updates.
```
[bluetooth]# register-characteristic\
4b75f0f8-1f23-46b1-900c-5bbabcd5ca93 encrypt-read,encrypt-notify
[NEW] Characteristic (Handle 0x0000)
/org/bluez/app/service0/chrc17
4b75f0f8-1f23-46b1-900c-5bbabcd5ca93
Vendor specific
[/org/bluez/app/service0/chrc17] Enter value: 42
```
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 | 52 ++++++++++++++++++++++++++++++++++++---------
1 file changed, 42 insertions(+), 10 deletions(-)
diff --git a/src/gatt-database.c b/src/gatt-database.c
index 68f411ba4..475e7873c 100644
--- a/src/gatt-database.c
+++ b/src/gatt-database.c
@@ -115,6 +115,7 @@ struct external_chrc {
uint8_t props;
uint8_t ext_props;
uint32_t perm;
+ uint32_t ccc_perm;
uint16_t mtu;
struct io *write_io;
struct io *notify_io;
@@ -1059,7 +1060,7 @@ static struct gatt_db_attribute *
service_add_ccc(struct gatt_db_attribute *service,
struct btd_gatt_database *database,
btd_gatt_database_ccc_write_t write_callback,
- void *user_data,
+ void *user_data, uint32_t perm,
btd_gatt_database_destroy_t destroy)
{
struct gatt_db_attribute *ccc;
@@ -1068,9 +1069,14 @@ service_add_ccc(struct gatt_db_attribute *service,
ccc_cb = new0(struct ccc_cb_data, 1);
+ /*
+ * Provide a way for the permissions on a characteristic to dictate
+ * the permissions on the CCC
+ */
+ perm |= BT_ATT_PERM_READ | BT_ATT_PERM_WRITE;
+
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, perm,
gatt_ccc_read_cb, gatt_ccc_write_cb, database);
if (!ccc) {
error("Failed to create CCC entry in database");
@@ -1227,7 +1233,7 @@ 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,
@@ -1633,11 +1639,18 @@ static bool incr_attr_count(struct external_service *service, uint16_t incr)
static bool parse_chrc_flags(DBusMessageIter *array, uint8_t *props,
uint8_t *ext_props, uint32_t *perm,
+ uint32_t *ccc_perm,
bool *req_prep_authorization)
{
const char *flag;
- *props = *ext_props = 0;
+ if (!props || !ext_props || !perm || !ccc_perm)
+ return false;
+
+ *props = 0;
+ *ext_props = 0;
+ *perm = 0;
+ *ccc_perm = 0;
do {
if (dbus_message_iter_get_arg_type(array) != DBUS_TYPE_STRING)
@@ -1690,6 +1703,24 @@ 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)) {
+ *ccc_perm |= BT_ATT_PERM_WRITE_ENCRYPT;
+ *props |= BT_GATT_CHRC_PROP_NOTIFY;
+ } else if (!strcmp("encrypt-authenticated-notify", flag)) {
+ *ccc_perm |= BT_ATT_PERM_WRITE_AUTHEN;
+ *props |= BT_GATT_CHRC_PROP_NOTIFY;
+ } else if (!strcmp("secure-notify", flag)) {
+ *ccc_perm |= BT_ATT_PERM_WRITE_SECURE;
+ *props |= BT_GATT_CHRC_PROP_NOTIFY;
+ } else if (!strcmp("encrypt-indicate", flag)) {
+ *ccc_perm |= BT_ATT_PERM_WRITE_ENCRYPT;
+ *props |= BT_GATT_CHRC_PROP_INDICATE;
+ } else if (!strcmp("encrypt-authenticated-indicate", flag)) {
+ *ccc_perm |= BT_ATT_PERM_WRITE_AUTHEN;
+ *props |= BT_GATT_CHRC_PROP_INDICATE;
+ } else if (!strcmp("secure-indicate", flag)) {
+ *ccc_perm |= BT_ATT_PERM_WRITE_SECURE;
+ *props |= BT_GATT_CHRC_PROP_INDICATE;
} else {
error("Invalid characteristic flag: %s", flag);
return false;
@@ -1743,7 +1774,8 @@ static bool parse_desc_flags(DBusMessageIter *array, uint32_t *perm,
}
static bool parse_flags(GDBusProxy *proxy, uint8_t *props, uint8_t *ext_props,
- uint32_t *perm, bool *req_prep_authorization)
+ uint32_t *perm, uint32_t *ccc_perm,
+ bool *req_prep_authorization)
{
DBusMessageIter iter, array;
const char *iface;
@@ -1760,7 +1792,7 @@ static bool parse_flags(GDBusProxy *proxy, uint8_t *props, uint8_t *ext_props,
if (!strcmp(iface, GATT_DESC_IFACE))
return parse_desc_flags(&array, perm, req_prep_authorization);
- return parse_chrc_flags(&array, props, ext_props, perm,
+ return parse_chrc_flags(&array, props, ext_props, perm, ccc_perm,
req_prep_authorization);
}
@@ -1810,7 +1842,7 @@ static struct external_chrc *chrc_create(struct gatt_app *app,
* created.
*/
if (!parse_flags(proxy, &chrc->props, &chrc->ext_props, &chrc->perm,
- &chrc->req_prep_authorization)) {
+ &chrc->ccc_perm, &chrc->req_prep_authorization)) {
error("Failed to parse characteristic properties");
goto fail;
}
@@ -1892,7 +1924,7 @@ static struct external_desc *desc_create(struct gatt_app *app,
* Parse descriptors flags here since they are used to
* determine the permission the descriptor should have
*/
- if (!parse_flags(proxy, NULL, NULL, &desc->perm,
+ if (!parse_flags(proxy, NULL, NULL, &desc->perm, NULL,
&desc->req_prep_authorization)) {
error("Failed to parse characteristic properties");
goto fail;
@@ -2796,7 +2828,7 @@ 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->ccc_perm, NULL);
if (!chrc->ccc) {
error("Failed to create CCC entry for characteristic");
return false;
--
2.31.1
