[meshcop] process ChannelMaskTlv in message (#3690)

Allows arbitrary number of Channel Mask entries.

src/core/meshcop/meshcop_tlvs.cpp

@@ -236,11 +236,39 @@ exit:
 
 uint32_t ChannelMaskTlv::GetChannelMask(const Message &aMessage)
 {
-    uint32_t       mask = 0;
+    uint32_t mask = 0;
-    ChannelMaskTlv channelMaskTlv;
+    uint16_t offset;
+    uint16_t end;
 
-    SuccessOrExit(GetTlv(aMessage, kChannelMask, sizeof(channelMaskTlv), channelMaskTlv));
+    SuccessOrExit(GetValueOffset(aMessage, kChannelMask, offset, end));
-    mask = channelMaskTlv.GetChannelMask();
+    end += offset;
+
+    while (offset + sizeof(ChannelMaskEntryBase) <= end)
+    {
+        ChannelMaskEntry entry;
+
+        aMessage.Read(offset, sizeof(ChannelMaskEntryBase), &entry);
+        VerifyOrExit(offset + entry.GetEntrySize() <= end);
+
+        switch (entry.GetChannelPage())
+        {
+#if OPENTHREAD_CONFIG_RADIO_2P4GHZ_OQPSK_SUPPORT
+        case OT_RADIO_CHANNEL_PAGE_0:
+            aMessage.Read(offset, sizeof(entry), &entry);
+            mask |= entry.GetMask() & OT_RADIO_2P4GHZ_OQPSK_CHANNEL_MASK;
+            break;
+#endif
+
+#if OPENTHREAD_CONFIG_RADIO_915MHZ_OQPSK_SUPPORT
+        case OT_RADIO_CHANNEL_PAGE_2:
+            aMessage.Read(offset, sizeof(entry), &entry);
+            mask |= entry.GetMask() & OT_RADIO_915MHZ_OQPSK_CHANNEL_MASK;
+            break;
+#endif
+        }
+
+        offset += entry.GetEntrySize();
+    }
 
 exit:
     return mask;