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fix signed overflow in ReadGlyph coordinate accumulation #200

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fix signed overflow in ReadGlyph coordinate accumulation #200

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28 changes: 24 additions & 4 deletions src/glyph.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,16 @@ static const int32_t kFLAG_WE_HAVE_AN_X_AND_Y_SCALE = 1 << 6;
static const int32_t kFLAG_WE_HAVE_A_TWO_BY_TWO = 1 << 7;
static const int32_t kFLAG_WE_HAVE_INSTRUCTIONS = 1 << 8;

bool SafeIntAddition(int a, int b, int* result) {
if (PREDICT_FALSE(
((a > 0) && (b > std::numeric_limits<int>::max() - a)) ||
((a < 0) && (b < std::numeric_limits<int>::min() - a)))) {
return false;
}
*result = a + b;
return true;
}

bool ReadCompositeGlyphData(Buffer* buffer, Glyph* glyph) {
glyph->have_instructions = false;
glyph->composite_data = buffer->buffer() + buffer->offset();
Expand Down Expand Up @@ -151,7 +161,10 @@ bool ReadGlyph(const uint8_t* data, size_t len, Glyph* glyph) {
return FONT_COMPRESSION_FAILURE();
}
int sign = (flag & kFLAG_XREPEATSIGN) ? 1 : -1;
glyph->contours[i][j].x = prev_x + sign * x_delta;
if (!SafeIntAddition(prev_x, sign * x_delta,
&glyph->contours[i][j].x)) {
return FONT_COMPRESSION_FAILURE();
}
} else {
// double byte x-delta coord value
int16_t x_delta = 0;
Expand All @@ -160,7 +173,9 @@ bool ReadGlyph(const uint8_t* data, size_t len, Glyph* glyph) {
return FONT_COMPRESSION_FAILURE();
}
}
glyph->contours[i][j].x = prev_x + x_delta;
if (!SafeIntAddition(prev_x, x_delta, &glyph->contours[i][j].x)) {
return FONT_COMPRESSION_FAILURE();
}
}
prev_x = glyph->contours[i][j].x;
}
Expand All @@ -178,7 +193,10 @@ bool ReadGlyph(const uint8_t* data, size_t len, Glyph* glyph) {
return FONT_COMPRESSION_FAILURE();
}
int sign = (flag & kFLAG_YREPEATSIGN) ? 1 : -1;
glyph->contours[i][j].y = prev_y + sign * y_delta;
if (!SafeIntAddition(prev_y, sign * y_delta,
&glyph->contours[i][j].y)) {
return FONT_COMPRESSION_FAILURE();
}
} else {
// double byte y-delta coord value
int16_t y_delta = 0;
Expand All @@ -187,7 +205,9 @@ bool ReadGlyph(const uint8_t* data, size_t len, Glyph* glyph) {
return FONT_COMPRESSION_FAILURE();
}
}
glyph->contours[i][j].y = prev_y + y_delta;
if (!SafeIntAddition(prev_y, y_delta, &glyph->contours[i][j].y)) {
return FONT_COMPRESSION_FAILURE();
}
}
prev_y = glyph->contours[i][j].y;
}
Expand Down