Disallow registering conflicting attribute access overrides.

src/app/AttributeAccessInterface.h

@@ -89,6 +89,16 @@ class AttributeAccessInterface
      */
     bool MatchesExactly(EndpointId aEndpointId) const { return mEndpointId.HasValue() && mEndpointId.Value() == aEndpointId; }
 
+    /**
+     * Check whether another AttributeAccessInterface wants to handle the same set of
+     * attributes as we do.
+     */
+    bool Matches(const AttributeAccessInterface & aOther) const
+    {
+        return mClusterId == aOther.mClusterId &&
+            (!mEndpointId.HasValue() || !aOther.mEndpointId.HasValue() || mEndpointId.Value() == aOther.mEndpointId.Value());
+    }
+
 private:
     Optional<EndpointId> mEndpointId;
     ClusterId mClusterId;

src/app/util/attribute-storage.cpp

@@ -42,6 +42,7 @@
 #include "app/util/common.h"
 #include <app/util/af.h>
 #include <app/util/attribute-storage.h>
+#include <lib/support/logging/CHIPLogging.h>
 
 #include <app-common/zap-generated/attribute-type.h>
 #include <app-common/zap-generated/callback.h>
@@ -1444,10 +1445,19 @@ bool emberAfExtractCommandIds(bool outgoing, EmberAfClusterCommand * cmd, Cluste
 }
 #endif
 
-void registerAttributeAccessOverride(app::AttributeAccessInterface * attrOverride)
+bool registerAttributeAccessOverride(app::AttributeAccessInterface * attrOverride)
 {
+    for (auto * cur = gAttributeAccessOverrides; cur; cur = cur->GetNext())
+    {
+        if (cur->Matches(*attrOverride))
+        {
+            ChipLogError(Zcl, "Duplicate attribute override registration failed");
+            return false;
+        }
+    }
     attrOverride->SetNext(gAttributeAccessOverrides);
     gAttributeAccessOverrides = attrOverride;
+    return true;
 }
 
 app::AttributeAccessInterface * findAttributeAccessOverride(EndpointId endpointId, ClusterId clusterId)

src/app/util/attribute-storage.h

@@ -259,9 +259,14 @@ uint16_t emberAfGetDynamicIndexFromEndpoint(chip::EndpointId id);
 /**
  * Register an attribute access override.  It will remain registered until
  * the endpoint it's registered for is disabled (or until shutdown if it's
- * registered for all endpoints).
+ * registered for all endpoints).  Registration will fail if there is an
+ * already-registered override for the same set of attributes.
+ *
+ * @return false if there is an existing override that the new one would
+ *               conflict with.  In this case the override is not registered.
+ * @return true if registration was successful.
  */
-void registerAttributeAccessOverride(chip::app::AttributeAccessInterface * attrOverride);
+bool registerAttributeAccessOverride(chip::app::AttributeAccessInterface * attrOverride);
 
 /**
  * Find an attribute access override, if any, that is registered for the given