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fix(gif): avoid int32 overflow in palette-split pixel-count math #5292

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Merged
lgritz merged 3 commits into from
Jul 6, 2026
+9 −6
Merged

fix(gif): avoid int32 overflow in palette-split pixel-count math #5292

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c71aba5
fix(gif): avoid int32 overflow in palette-split pixel-count math
lgritz Jul 3, 2026
63ded65
More overflow protection
lgritz Jul 5, 2026
3027b7d
fix formatting
lgritz Jul 5, 2026
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7 changes: 4 additions & 3 deletions src/gif.imageio/gif.h
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Original file line number Diff line number Diff line change
Expand Up @@ -340,7 +340,8 @@ void GifSplitPalette(uint8_t* image, int numPixels, int firstElt, int lastElt, i
if(bRange > gRange) splitCom = 2;
if(rRange > bRange && rRange > gRange) splitCom = 0;

int subPixelsA = numPixels * (splitElt - firstElt) / (lastElt - firstElt);
int subPixelsA = (int)(int64_t(numPixels) * (splitElt - firstElt)
/ (lastElt - firstElt));
int subPixelsB = numPixels-subPixelsA;

GifPartitionByMedian(image, 0, numPixels, splitCom, subPixelsA);
Expand Down Expand Up @@ -388,7 +389,7 @@ void GifMakePalette( const uint8_t* lastFrame, const uint8_t* nextFrame, uint32_

// SplitPalette is destructive (it sorts the pixels by color) so
// we must create a copy of the image for it to destroy
size_t imageSize = (size_t)(width * height * 4 * sizeof(uint8_t));
size_t imageSize = size_t(width) * size_t(height) * 4 * sizeof(uint8_t);
uint8_t* destroyableImage = (uint8_t*)GIF_TEMP_MALLOC(imageSize);
memcpy(destroyableImage, nextFrame, imageSize);

Expand Down Expand Up @@ -789,7 +790,7 @@ bool GifBegin( GifWriter<FILE>* writer, const char* filename, uint32_t width, ui
writer->firstFrame = true;

// allocate
writer->oldImage = (uint8_t*)GIF_MALLOC(width*height*4);
writer->oldImage = (uint8_t*)GIF_MALLOC(uint64_t(width)*uint64_t(height)*4);

fputs("GIF89a", writer->f);

Expand Down
8 changes: 5 additions & 3 deletions src/gif.imageio/gifinput.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,8 @@ GIFInput::read_native_scanline(int subimage, int miplevel, int y, int /*z*/,
if (y < 0 || y > m_spec.height || !m_canvas.size())
return false;

memcpy(data, &m_canvas[y * m_spec.width * m_spec.nchannels],
memcpy(data,
&m_canvas[int64_t(y) * int64_t(m_spec.width) * m_spec.nchannels],
m_spec.width * m_spec.nchannels);

return true;
Expand Down Expand Up @@ -365,8 +366,9 @@ GIFInput::read_subimage_data()
fscanline[wx], wx, y, colormap_count);
return false;
}
int x = window_left + wx;
int idx = m_spec.nchannels * (y * m_spec.width + x);
int x = window_left + wx;
int64_t idx = m_spec.nchannels
* (int64_t(y) * m_spec.width + x);
if (0 <= x && x < m_spec.width) {
m_canvas[idx] = colormap[fscanline[wx]].Red;
m_canvas[idx + 1] = colormap[fscanline[wx]].Green;
Expand Down
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