StandalonePluginHolder: Fix out-of-bounds read when audio callbacks use larger-than-expected buffers

Author: reuk

modules/juce_audio_plugin_client/Standalone/juce_StandaloneFilterWindow.h

@@ -408,6 +408,91 @@ class StandalonePluginHolder    : private AudioIODeviceCallback,
     Array<MidiDeviceInfo> lastMidiDevices;
 
 private:
+    /*  This class can be used to ensure that audio callbacks use buffers with a
+        predictable maximum size.
+
+        On some platforms (such as iOS 10), the expected buffer size reported in
+        audioDeviceAboutToStart may be smaller than the blocks passed to
+        audioDeviceIOCallback. This can lead to out-of-bounds reads if the render
+        callback depends on additional buffers which were initialised using the
+        smaller size.
+
+        As a workaround, this class will ensure that the render callback will
+        only ever be called with a block with a length less than or equal to the
+        expected block size.
+    */
+    class CallbackMaxSizeEnforcer  : public AudioIODeviceCallback
+    {
+    public:
+        explicit CallbackMaxSizeEnforcer (AudioIODeviceCallback& callbackIn)
+            : inner (callbackIn) {}
+
+        void audioDeviceAboutToStart (AudioIODevice* device) override
+        {
+            maximumSize = device->getCurrentBufferSizeSamples();
+            storedInputChannels .resize ((size_t) device->getActiveInputChannels() .countNumberOfSetBits());
+            storedOutputChannels.resize ((size_t) device->getActiveOutputChannels().countNumberOfSetBits());
+
+            inner.audioDeviceAboutToStart (device);
+        }
+
+        void audioDeviceIOCallback (const float** inputChannelData,
+                                    int numInputChannels,
+                                    float** outputChannelData,
+                                    int numOutputChannels,
+                                    int numSamples) override
+        {
+            jassert ((int) storedInputChannels.size()  == numInputChannels);
+            jassert ((int) storedOutputChannels.size() == numOutputChannels);
+            ignoreUnused (numInputChannels, numOutputChannels);
+
+            int position = 0;
+
+            while (position < numSamples)
+            {
+                const auto blockLength = jmin (maximumSize, numSamples - position);
+
+                initChannelPointers (inputChannelData,  storedInputChannels,  position);
+                initChannelPointers (outputChannelData, storedOutputChannels, position);
+
+                inner.audioDeviceIOCallback (storedInputChannels.data(),
+                                             (int) storedInputChannels.size(),
+                                             storedOutputChannels.data(),
+                                             (int) storedOutputChannels.size(),
+                                             blockLength);
+
+                position += blockLength;
+            }
+        }
+
+        void audioDeviceStopped() override
+        {
+            inner.audioDeviceStopped();
+        }
+
+    private:
+        struct GetChannelWithOffset
+        {
+            int offset;
+
+            template <typename Ptr>
+            auto operator() (Ptr ptr) const noexcept -> Ptr { return ptr + offset; }
+        };
+
+        template <typename Ptr, typename Vector>
+        void initChannelPointers (Ptr&& source, Vector&& target, int offset)
+        {
+            std::transform (source, source + target.size(), target.begin(), GetChannelWithOffset { offset });
+        }
+
+        AudioIODeviceCallback& inner;
+        int maximumSize = 0;
+        std::vector<const float*> storedInputChannels;
+        std::vector<float*> storedOutputChannels;
+    };
+
+    CallbackMaxSizeEnforcer maxSizeEnforcer { *this };
+
     //==============================================================================
     class SettingsComponent : public Component
     {
@@ -533,7 +618,7 @@ class StandalonePluginHolder    : private AudioIODeviceCallback,
                             const String& preferredDefaultDeviceName,
                             const AudioDeviceManager::AudioDeviceSetup* preferredSetupOptions)
     {
-        deviceManager.addAudioCallback (this);
+        deviceManager.addAudioCallback (&maxSizeEnforcer);
         deviceManager.addMidiInputDeviceCallback ({}, &player);
 
         reloadAudioDeviceState (enableAudioInput, preferredDefaultDeviceName, preferredSetupOptions);
@@ -544,7 +629,7 @@ class StandalonePluginHolder    : private AudioIODeviceCallback,
         saveAudioDeviceState();
 
         deviceManager.removeMidiInputDeviceCallback ({}, &player);
-        deviceManager.removeAudioCallback (this);
+        deviceManager.removeAudioCallback (&maxSizeEnforcer);
     }
 
     void timerCallback() override