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read: add bounds checks during extent merge to prevent buffer overflow #3004

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read: add bounds checks during extent merge to prevent buffer overflow #3004

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4d1f8ef
read: add bounds checks during extent merge to prevent buffer overflow
Naveed8951 Feb 5, 2026
d0b72c6
use INTERNAL_ERROR and simplify overflow check during extent merge
Naveed8951 Feb 6, 2026
4ac4fff
switch extent merge overflow checks to assertions and use writeOffset
Naveed8951 Feb 7, 2026
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12 changes: 9 additions & 3 deletions src/read.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1534,9 +1534,15 @@ static avifResult avifDecoderItemRead(avifDecoderItem * item,
item->mergedExtents.size = bytesToRead;
} else {
AVIF_ASSERT_OR_RETURN(item->ownsMergedExtents);
AVIF_ASSERT_OR_RETURN(front);
memcpy(front, offsetBuffer.data, bytesToRead);
front += bytesToRead;

size_t writeOffset = (size_t)(front - item->mergedExtents.data);
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@wantehchang wantehchang Feb 7, 2026

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With the checks / assertions you are adding, the writeOffset variable is more convenient than the front variable.

I suggest replacing the front variable with the writeOffset variable. Then in the memcpy() call below, recover front by using item->mergedExtents.data + writeOffset.


AVIF_ASSERT_OR_RETURN(writeOffset < item->mergedExtents.size);
AVIF_ASSERT_OR_RETURN(bytesToRead <= item->mergedExtents.size - writeOffset);

uint8_t *dst = item->mergedExtents.data + writeOffset;
memcpy(dst, offsetBuffer.data, bytesToRead);
writeOffset += bytesToRead;
}

remainingBytes -= bytesToRead;
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