net: lwm2m: Remove .well-known/core handling

`.well-known/core` resource is described by the CoAP RFC as an optional
method of resource discovery. The LwM2M specification though makes no
mentionon about this mechanism and provides an alternative method of
resource discovery instead (Device Management Discover, sec 5.4.2, and
Bootstrap Discovery, sec 5.2.7.3).

Since LwM2M does not require to implement `.well-known/core` resource
and it complicates the existing Discovery mechanism (and likely cause a
security concern) remove its handling from the LwM2M implementation.

Signed-off-by: Robert Lubos <[email protected]>

Author: rlubos

subsys/net/lib/lwm2m/lwm2m_engine.c

@@ -59,8 +59,6 @@ LOG_MODULE_REGISTER(LOG_MODULE_NAME);
 #define ENGINE_UPDATE_INTERVAL_MS 500
 #define OBSERVE_COUNTER_START 0U
 
-#define WELL_KNOWN_CORE_PATH	"</.well-known/core>"
-
 /*
  * TODO: to implement a way for clients to specify alternate path
  * via Kconfig (LwM2M specification 8.2.2 Alternate Path)
@@ -3316,20 +3314,18 @@ static int print_resource_dimension(struct lwm2m_output_context *out,
 	return 0;
 }
 
-static int do_discover_op(struct lwm2m_message *msg, bool well_known)
+static int do_discover_op(struct lwm2m_message *msg)
 {
 	static char disc_buf[24];
 	struct lwm2m_engine_obj *obj;
 	struct lwm2m_engine_obj_inst *obj_inst;
 	int ret;
 	bool reported = false;
 
-	/* object ID is required unless it's a ".well-known/core" discovery
-	 * ref: lwm2m spec 20170208-A table 11
+	/* object ID is required in Device Management Discovery (5.4.2).
 	 */
-	if (!well_known &&
-	    (msg->path.level == 0U ||
-	     msg->path.obj_id == LWM2M_OBJECT_SECURITY_ID)) {
+	if (msg->path.level == 0U ||
+	    msg->path.obj_id == LWM2M_OBJECT_SECURITY_ID) {
 		return -EPERM;
 	}
 
@@ -3347,30 +3343,6 @@ static int do_discover_op(struct lwm2m_message *msg, bool well_known)
 		return ret;
 	}
 
-	/* Handle CoAP .well-known/core discover */
-	if (well_known) {
-		/* </.well-known/core> */
-		ret = buf_append(CPKT_BUF_WRITE(msg->out.out_cpkt),
-				 WELL_KNOWN_CORE_PATH,
-				 strlen(WELL_KNOWN_CORE_PATH));
-		if (ret < 0) {
-			return ret;
-		}
-
-		SYS_SLIST_FOR_EACH_CONTAINER(&engine_obj_list, obj, node) {
-			snprintk(disc_buf, sizeof(disc_buf), ",</%u>",
-				 obj->obj_id);
-
-			ret = buf_append(CPKT_BUF_WRITE(msg->out.out_cpkt),
-					 disc_buf, strlen(disc_buf));
-			if (ret < 0) {
-				return ret;
-			}
-		}
-
-		return 0;
-	}
-
 	/* Report object attributes only when Object ID (alone) was
 	 * provided (and do it only once in case of multiple instances).
 	 */
@@ -3812,7 +3784,6 @@ static int handle_request(struct coap_packet *request,
 	uint8_t tkl = 0U;
 	uint16_t format = LWM2M_FORMAT_NONE, accept;
 	int observe = -1; /* default to -1, 0 = ENABLE, 1 = DISABLE */
-	bool well_known = false;
 	int block_opt, block_num;
 	struct lwm2m_block_context *block_ctx = NULL;
 	enum coap_block_size block_size;
@@ -3872,22 +3843,10 @@ static int handle_request(struct coap_packet *request,
 		}
 	}
 
-	/* check for .well-known/core URI query (DISCOVER) */
-	if (r == 2 &&
-	    (options[0].len == 11U &&
-	     strncmp(options[0].value, ".well-known", 11) == 0) &&
-	    (options[1].len == 4U &&
-	     strncmp(options[1].value, "core", 4) == 0)) {
-		if ((code & COAP_REQUEST_MASK) != COAP_METHOD_GET) {
-			r = -EPERM;
-			goto error;
-		}
-
-		well_known = true;
 #if defined(CONFIG_LWM2M_RD_CLIENT_SUPPORT_BOOTSTRAP)
 	/* check for bootstrap-finish */
-	} else if ((code & COAP_REQUEST_MASK) == COAP_METHOD_POST && r == 1 && \
-		   strncmp(options[0].value, "bs", options[0].len) == 0) {
+	if ((code & COAP_REQUEST_MASK) == COAP_METHOD_POST && r == 1 &&
+	    strncmp(options[0].value, "bs", options[0].len) == 0) {
 		engine_bootstrap_finish();
 
 		msg->code = COAP_RESPONSE_CODE_CHANGED;
@@ -3898,8 +3857,9 @@ static int handle_request(struct coap_packet *request,
 		}
 
 		return 0;
+	} else
 #endif
-	} else {
+	{
 		r = coap_options_to_path(options, r, &msg->path);
 		if (r < 0) {
 			r = -ENOENT;
@@ -3932,8 +3892,7 @@ static int handle_request(struct coap_packet *request,
 		goto error;
 	}
 
-	if (!well_known && !(msg->ctx->bootstrap_mode &&
-			     msg->path.level == 0)) {
+	if (!(msg->ctx->bootstrap_mode && msg->path.level == 0)) {
 		/* find registered obj */
 		obj = get_engine_obj(msg->path.obj_id);
 		if (!obj) {
@@ -3951,7 +3910,7 @@ static int handle_request(struct coap_packet *request,
 		 * LwM2M V1_0_1-20170704-A, table 25,
 		 * Discover: CoAP GET + accept=LWM2M_FORMAT_APP_LINK_FORMAT
 		 */
-		if (well_known || accept == LWM2M_FORMAT_APP_LINK_FORMAT) {
+		if (accept == LWM2M_FORMAT_APP_LINK_FORMAT) {
 			msg->operation = LWM2M_OP_DISCOVER;
 			accept = LWM2M_FORMAT_APP_LINK_FORMAT;
 		} else {
@@ -4121,7 +4080,7 @@ static int handle_request(struct coap_packet *request,
 				break;
 			}
 #endif
-			r = do_discover_op(msg, well_known);
+			r = do_discover_op(msg);
 			break;
 
 		case LWM2M_OP_WRITE: