[bbr] validate BBR configuration (#5221)

This commit makes sure BBR configuration is valid according to Thread
Spec 5.21.3.3.

include/openthread/backbone_router_ftd.h

@@ -115,13 +115,16 @@ void otBackboneRouterGetConfig(otInstance *aInstance, otBackboneRouterConfig *aC
  * @param[in]  aInstance             A pointer to an OpenThread instance.
  * @param[in]  aConfig               A pointer to the Backbone Router configuration to take effect.
  *
+ * @retval OT_ERROR_NONE          Successfully updated configuration.
+ * @retval OT_ERROR_INVALID_ARGS  The configuration in @p aConfig is invalid.
+ *
  * @sa otBackboneRouterSetEnabled
  * @sa otBackboneRouterGetState
  * @sa otBackboneRouterGetConfig
  * @sa otBackboneRouterRegister
  *
  */
-void otBackboneRouterSetConfig(otInstance *aInstance, const otBackboneRouterConfig *aConfig);
+otError otBackboneRouterSetConfig(otInstance *aInstance, const otBackboneRouterConfig *aConfig);
 
 /**
  * This function explicitly registers local Backbone Router configuration.

include/openthread/instance.h

@@ -53,7 +53,7 @@ extern "C" {
  * @note This number versions both OpenThread platform and user APIs.
  *
  */
-#define OPENTHREAD_API_VERSION (13)
+#define OPENTHREAD_API_VERSION (14)
 
 /**
  * @addtogroup api-instance

src/cli/cli.cpp

@@ -582,7 +582,7 @@ otError Interpreter::ProcessBackboneRouterLocal(uint8_t aArgsLength, char *aArgs
                 }
             }
 
-            otBackboneRouterSetConfig(mInstance, &config);
+            SuccessOrExit(error = otBackboneRouterSetConfig(mInstance, &config));
         }
     }
     else

src/core/api/backbone_router_ftd_api.cpp

@@ -64,13 +64,13 @@ void otBackboneRouterGetConfig(otInstance *aInstance, otBackboneRouterConfig *aC
     instance.Get<BackboneRouter::Local>().GetConfig(*aConfig);
 }
 
-void otBackboneRouterSetConfig(otInstance *aInstance, const otBackboneRouterConfig *aConfig)
+otError otBackboneRouterSetConfig(otInstance *aInstance, const otBackboneRouterConfig *aConfig)
 {
     Instance &instance = *static_cast<Instance *>(aInstance);
 
     OT_ASSERT(aConfig != nullptr);
 
-    instance.Get<BackboneRouter::Local>().SetConfig(*aConfig);
+    return instance.Get<BackboneRouter::Local>().SetConfig(*aConfig);
 }
 
 otError otBackboneRouterRegister(otInstance *aInstance)

src/core/backbone_router/local.cpp

@@ -137,9 +137,18 @@ void Local::GetConfig(BackboneRouterConfig &aConfig) const
     aConfig.mMlrTimeout          = mMlrTimeout;
 }
 
-void Local::SetConfig(const BackboneRouterConfig &aConfig)
+otError Local::SetConfig(const BackboneRouterConfig &aConfig)
 {
-    bool update = false;
+    otError error  = OT_ERROR_NONE;
+    bool    update = false;
+
+    VerifyOrExit(aConfig.mMlrTimeout >= Mle::kMlrTimeoutMin, error = OT_ERROR_INVALID_ARGS);
+    // Validate configuration according to Thread 1.2.1 Specification 5.21.3.3:
+    // "The Reregistration Delay in seconds MUST be lower than (0.5 * MLR Timeout). It MUST be at least 1."
+    VerifyOrExit(aConfig.mReregistrationDelay >= 1, error = OT_ERROR_INVALID_ARGS);
+    static_assert(sizeof(aConfig.mReregistrationDelay) < sizeof(aConfig.mMlrTimeout),
+                  "the calculation below might overflow");
+    VerifyOrExit(aConfig.mReregistrationDelay * 2 < aConfig.mMlrTimeout, error = OT_ERROR_INVALID_ARGS);
 
     if (aConfig.mReregistrationDelay != mReregistrationDelay)
     {
@@ -169,7 +178,9 @@ void Local::SetConfig(const BackboneRouterConfig &aConfig)
         }
     }
 
-    LogBackboneRouterService("Set", OT_ERROR_NONE);
+exit:
+    LogBackboneRouterService("Set", error);
+    return error;
 }
 
 otError Local::AddService(bool aForce)

src/core/backbone_router/local.hpp

@@ -104,8 +104,11 @@ public:
      *
      * @param[in]  aConfig  The configuration to set.
      *
+     * @retval OT_ERROR_NONE          Successfully updated configuration.
+     * @retval OT_ERROR_INVALID_ARGS  The configuration in @p aConfig is invalid.
+     *
      */
-    void SetConfig(const BackboneRouterConfig &aConfig);
+    otError SetConfig(const BackboneRouterConfig &aConfig);
 
     /**
      * This method registers Backbone Router Dataset to Leader.

src/core/thread/mle_types.hpp

@@ -258,9 +258,13 @@ enum
 {
     kRegistrationDelayDefault         = 1200, //< In seconds.
     kMlrTimeoutDefault                = 3600, //< In seconds.
+    kMlrTimeoutMin                    = 300,  //< In seconds.
     kBackboneRouterRegistrationJitter = 5,    //< In seconds.
 };
 
+static_assert(kMlrTimeoutDefault >= kMlrTimeoutMin,
+              "kMlrTimeoutDefault must be larger than or equal to kMlrTimeoutMin");
+
 #endif
 
 /**