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Fix integer overflow in StationTessellatorImpl buffer growth #262

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Fix integer overflow in StationTessellatorImpl buffer growth #262

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24 changes: 19 additions & 5 deletions ...in/java/net/modificationstation/stationapi/impl/client/render/StationTessellatorImpl.java
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,12 @@

public class StationTessellatorImpl implements StationTessellator {

// Hard ceiling on the int-buffer size so it can never grow large enough for
// bufferSize * 4 (the byte-buffer allocation) to overflow a signed int.
// 2^28 ints = 1 GiB direct buffer, far beyond anything vanilla rendering needs;
// the buffer base size is 2^21 ints, so this still allows several doublings.
private static final int MAX_BUFFER_SIZE = 1 << 28;

private final Tessellator self;
private final TessellatorAccessor access;
private final int[] fastVertexData = new int[32];
Expand Down Expand Up @@ -103,11 +109,19 @@ public void quad(BakedQuad quad, float x, float y, float z, int colour0, int col

@Override
public void ensureBufferCapacity(int criticalCapacity) {
if (access.stationapi$getBufferPosition() >= access.stationapi$getBufferSize() - criticalCapacity) {
LOGGER.info("Tessellator is nearing its maximum capacity. Increasing the buffer size from {} to {}", access.stationapi$getBufferSize(), access.stationapi$getBufferSize() * 2);
access.stationapi$setBufferSize(access.stationapi$getBufferSize() * 2);
access.stationapi$setBuffer(Arrays.copyOf(access.stationapi$getBuffer(), access.stationapi$getBufferSize()));
ByteBuffer newBuffer = GlAllocationUtils.allocateByteBuffer(access.stationapi$getBufferSize() * 4);
int bufferSize = access.stationapi$getBufferSize();
if (access.stationapi$getBufferPosition() >= bufferSize - criticalCapacity) {
if (bufferSize >= MAX_BUFFER_SIZE) {
// Already at the ceiling; doubling further would overflow bufferSize * 4.
// Leave the buffer as-is rather than allocating an invalid (negative) capacity.
return;
}
int newBufferSize = Math.min(bufferSize * 2, MAX_BUFFER_SIZE);
LOGGER.info("Tessellator is nearing its maximum capacity. Increasing the buffer size from {} to {}", bufferSize, newBufferSize);
access.stationapi$setBufferSize(newBufferSize);
access.stationapi$setBuffer(Arrays.copyOf(access.stationapi$getBuffer(), newBufferSize));
// long arithmetic so the byte count can never overflow a signed int.
ByteBuffer newBuffer = GlAllocationUtils.allocateByteBuffer((int) ((long) newBufferSize * 4));

@mineLdiver mineLdiver Aug 1, 2026

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Not sure how long helps here if it's casted to int immediately after. Plus, isn't everything that's calculated before prevents newBufferSize * 4 from ever overflowing in the first place?

access.stationapi$setByteBuffer(newBuffer);
access.stationapi$setIntBuffer(newBuffer.asIntBuffer());
access.stationapi$setFloatBuffer(newBuffer.asFloatBuffer());
Expand Down