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st: Avoid integer overflow on unpremultiply

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When computing the effective border color, we operate on colors with
premultiplied alpha to simplify the calculations, then unpremultiply
the result. However we miss a bounds check in the last check, so any
color component can overflow the allowed maximum of 0xff and shift the
result in unexpected ways.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/305

(cherry picked from commit 925a25da17)
This commit is contained in:
Florian Müllner 2018-11-22 20:41:44 +01:00 committed by Marco Trevisan (Treviño)
parent fa2ddcc52f
commit b29e243fec
1 changed files with 3 additions and 3 deletions
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6
src/st/st-theme-node-drawing.c
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@ -229,9 +229,9 @@ unpremultiply (ClutterColor *color)
{
if (color->alpha != 0)
{
color->red = (color->red * 255 + 127) / color->alpha;
color->green = (color->green * 255 + 127) / color->alpha;
color->blue = (color->blue * 255 + 127) / color->alpha;
color->red = MIN((color->red * 255 + 127) / color->alpha, 255);
color->green = MIN((color->green * 255 + 127) / color->alpha, 255);
color->blue = MIN((color->blue * 255 + 127) / color->alpha, 255);
}
}