[border-router] add validation of updated on mesh prefixes (#6313)

This commit adds validation of the on mesh prefixes.

With this change, the domain on mesh prefix can be directly configured
after successful verification.

src/core/api/border_router_api.cpp

@@ -80,18 +80,17 @@ otError otBorderRouterAddOnMeshPrefix(otInstance *aInstance, const otBorderRoute
 
     OT_ASSERT(aConfig != nullptr);
 
-    SuccessOrExit(error = instance.Get<NetworkData::Local>().AddOnMeshPrefix(*config));
-
 #if OPENTHREAD_FTD && OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE
-    // Only try to configure Domain Prefix after the parameter is validated via above `AddOnMeshPrefix()`.
     if (aConfig->mDp)
     {
-        // Restore local server data
-        IgnoreError(instance.Get<NetworkData::Local>().RemoveOnMeshPrefix(config->GetPrefix()));
-
+        SuccessOrExit(error = instance.Get<NetworkData::Local>().ValidateOnMeshPrefix(*config));
         instance.Get<BackboneRouter::Local>().SetDomainPrefix(*config);
     }
+    else
 #endif
+    {
+        SuccessOrExit(error = instance.Get<NetworkData::Local>().AddOnMeshPrefix(*config));
+    }
 
 exit:
     return error;

src/core/thread/network_data_local.cpp

@@ -54,10 +54,9 @@ Local::Local(Instance &aInstance)
 }
 
 #if OPENTHREAD_CONFIG_BORDER_ROUTER_ENABLE
-Error Local::AddOnMeshPrefix(const OnMeshPrefixConfig &aConfig)
+Error Local::ValidateOnMeshPrefix(const OnMeshPrefixConfig &aConfig)
 {
-    Error    error;
-    uint16_t flags = 0;
+    Error error = kErrorNone;
 
     // Add Prefix validation check:
     // Thread 1.1 Specification 5.13.2 says
@@ -69,6 +68,19 @@ Error Local::AddOnMeshPrefix(const OnMeshPrefixConfig &aConfig)
     // of an IEEE 802.15.4 interface MUST have a length of 64 bits.
     VerifyOrExit(!aConfig.mSlaac || aConfig.mPrefix.mLength == OT_IP6_PREFIX_BITSIZE, error = kErrorInvalidArgs);
 
+    SuccessOrExit(error = ValidatePrefixAndPreference(aConfig.GetPrefix(), aConfig.mPreference));
+
+exit:
+    return error;
+}
+
+Error Local::AddOnMeshPrefix(const OnMeshPrefixConfig &aConfig)
+{
+    uint16_t flags = 0;
+    Error    error = kErrorNone;
+
+    SuccessOrExit(error = ValidateOnMeshPrefix(aConfig));
+
     if (aConfig.mPreferred)
     {
         flags |= BorderRouterEntry::kPreferredFlag;
@@ -123,6 +135,28 @@ Error Local::RemoveOnMeshPrefix(const Ip6::Prefix &aPrefix)
     return RemovePrefix(aPrefix, NetworkDataTlv::kTypeBorderRouter);
 }
 
+Error Local::ValidatePrefixAndPreference(const Ip6::Prefix &aPrefix, int8_t aPrf)
+{
+    Error error = kErrorNone;
+
+    VerifyOrExit((aPrefix.GetLength() > 0) && aPrefix.IsValid(), error = kErrorInvalidArgs);
+
+    switch (aPrf)
+    {
+    case OT_ROUTE_PREFERENCE_LOW:
+    case OT_ROUTE_PREFERENCE_MED:
+    case OT_ROUTE_PREFERENCE_HIGH:
+        break;
+    default:
+        ExitNow(error = kErrorInvalidArgs);
+    }
+
+    // Check if the prefix overlaps mesh-local prefix.
+    VerifyOrExit(!aPrefix.ContainsPrefix(Get<Mle::MleRouter>().GetMeshLocalPrefix()), error = kErrorInvalidArgs);
+exit:
+    return error;
+}
+
 Error Local::AddHasRoutePrefix(const ExternalRouteConfig &aConfig)
 {
     return AddPrefix(aConfig.GetPrefix(), NetworkDataTlv::kTypeHasRoute, aConfig.mPreference, /* aFlags */ 0,
@@ -144,19 +178,7 @@ Error Local::AddPrefix(const Ip6::Prefix &  aPrefix,
     uint8_t    subTlvLength;
     PrefixTlv *prefixTlv;
 
-    VerifyOrExit((aPrefix.GetLength() > 0) && aPrefix.IsValid(), error = kErrorInvalidArgs);
-
-    switch (aPrf)
-    {
-    case OT_ROUTE_PREFERENCE_LOW:
-    case OT_ROUTE_PREFERENCE_MED:
-    case OT_ROUTE_PREFERENCE_HIGH:
-        break;
-    default:
-        ExitNow(error = kErrorInvalidArgs);
-    }
-
-    VerifyOrExit(!aPrefix.ContainsPrefix(Get<Mle::MleRouter>().GetMeshLocalPrefix()), error = kErrorInvalidArgs);
+    SuccessOrExit(error = ValidatePrefixAndPreference(aPrefix, aPrf));
 
     IgnoreError(RemovePrefix(aPrefix, aSubTlvType));
 

src/core/thread/network_data_local.hpp

@@ -83,6 +83,17 @@ public:
      */
     Error AddOnMeshPrefix(const OnMeshPrefixConfig &aConfig);
 
+    /**
+     * This method validates an on-mesh prefix.
+     *
+     * @param[in]  aConfig        A reference to the on-mesh perfix configuration.
+     *
+     * @retval kErrorNone         Successfully verified the on-mesh prefix.
+     * @retval kErrorInvalidArgs  The prefix is not a valid on-mesh prefix.
+     *
+     */
+    Error ValidateOnMeshPrefix(const OnMeshPrefixConfig &aConfig);
+
     /**
      * This method removes a Border Router entry from the Thread Network Data.
      *
@@ -170,6 +181,7 @@ public:
 private:
     void UpdateRloc(void);
 #if OPENTHREAD_CONFIG_BORDER_ROUTER_ENABLE
+    Error ValidatePrefixAndPreference(const Ip6::Prefix &aPrefix, int8_t aPrf);
     Error AddPrefix(const Ip6::Prefix &  aPrefix,
                     NetworkDataTlv::Type aSubTlvType,
                     int8_t               aPrf,