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Fix memory-amplification DoS via uint16 underflow in ReadGlyph #190

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Fix memory-amplification DoS via uint16 underflow in ReadGlyph #190

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6 changes: 6 additions & 0 deletions src/glyph.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,12 @@ bool ReadGlyph(const uint8_t* data, size_t len, Glyph* glyph) {
if (!buffer.ReadU16(&point_index)) {
return FONT_COMPRESSION_FAILURE();
}
// endPtsOfContours must be monotonically increasing per the TrueType
// spec. A decreasing value wraps the uint16 subtraction below, causing
// huge allocations from small inputs (memory-amplification DoS).
if (i > 0 && point_index < last_point_index) {
return FONT_COMPRESSION_FAILURE();
}
uint16_t num_points = point_index - last_point_index + (i == 0 ? 1 : 0);
glyph->contours[i].resize(num_points);
last_point_index = point_index;
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