Skip to content

fix: zeroObject double-far pointer deref #151

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
dwrensha merged 1 commit into from
Jan 14, 2026
Merged

fix: zeroObject double-far pointer deref #151

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 2 additions & 2 deletions runtime/src/main/java/org/capnproto/WireHelpers.java
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -203,9 +203,9 @@ static void zeroObject(SegmentBuilder segment, int refOffset) {
int padOffset = FarPointer.positionInSegment(ref);
long pad = segment.get(padOffset);
if (FarPointer.isDoubleFar(ref)) {
SegmentBuilder otherSegment = segment.getArena().getSegment(FarPointer.getSegmentId(ref));
SegmentBuilder otherSegment = segment.getArena().getSegment(FarPointer.getSegmentId(pad));
if (otherSegment.isWritable()) {
zeroObject(otherSegment, padOffset + 1, FarPointer.positionInSegment(pad));
zeroObject(otherSegment, segment.get(padOffset + 1), FarPointer.positionInSegment(pad));
}
segment.buffer.putLong(padOffset * 8, 0L);
segment.buffer.putLong((padOffset + 1) * 8, 0L);
Expand Down
94 changes: 94 additions & 0 deletions runtime/src/test/java/org/capnproto/LayoutTest.java
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

import static org.junit.jupiter.api.Assertions.assertArrayEquals;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

Expand Down Expand Up @@ -181,4 +182,97 @@ private void checkStruct(StructBuilder builder) {
assertEquals(true, builder._getBooleanField(126));
assertEquals(false, builder._getBooleanField(127));
}

@Test
public void testWireHelpersZeroObjectFarPointer() {
byte ffff = (byte)0xff;
byte[][] segments;
byte[][] expect;

segments = new byte[][] {
{
// Far pointer, offset = 2, segment id = 1.
0x12, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
{
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
// Landing pad, offset = 1, list of 6 bytes.
0x05, 0x00, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
// List data.
0x01, 0x02, 0x03, 0x04, 0x05, 0x06, ffff, ffff,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
};
expect = new byte[][] {
{
0x12, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
{
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
};
doTestWireHelpersZeroObject(segments, expect);

segments = new byte[][] {
{
// Double-far pointer, offset = 2, segment id = 1.
0x16, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
{
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
// Landing pad far pointer, offset = 1, segment id = 2.
0x0e, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00,
// Landing pad tag, list of 6 bytes.
0x01, 0x00, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
{
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
// List data.
0x01, 0x02, 0x03, 0x04, 0x05, 0x06, ffff, ffff,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
};
expect = new byte[][] {
{
0x16, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
{
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
{
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
ffff, ffff, ffff, ffff, ffff, ffff, ffff, ffff,
},
};
doTestWireHelpersZeroObject(segments, expect);
}

private void doTestWireHelpersZeroObject(byte[][] segments, byte[][] expect) {
ByteBuffer[] buffers = new ByteBuffer[segments.length];
for (int i = 0; i < segments.length; i++) {
buffers[i] = ByteBuffer.wrap(segments[i]);
buffers[i].order(ByteOrder.LITTLE_ENDIAN);
}
BuilderArena arena = new BuilderArena(new ReaderArena(buffers, 0x7fffffffffffffffL));
WireHelpers.zeroObject(arena.getSegment(0), 0);
assertArrayEquals(expect, segments);
}
}