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Fix GH-16559: UBSan abort in ext/gd/libgd/gd_interpolation.c:1007 #16562

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24 changes: 18 additions & 6 deletions ext/gd/libgd/gd_interpolation.c
Original file line number Diff line number Diff line change
Expand Up @@ -929,21 +929,29 @@ static inline LineContribType *_gdContributionsCalc(unsigned int line_size, unsi
return res;
}

/* Convert a double to an unsigned char, rounding to the nearest
* integer and clamping the result between 0 and max. The absolute
* value of clr must be less than the maximum value of an unsigned
* short. */
static inline unsigned char
uchar_clamp(double clr) {
uchar_clamp(double clr, unsigned char max) {
unsigned short result;
assert(fabs(clr) <= SHRT_MAX);

//assert(fabs(clr) <= SHRT_MAX);

/* Casting a negative float to an unsigned short is undefined.
* However, casting a float to a signed truncates toward zero and
* casting a negative signed value to an unsigned of the same size
* results in a bit-identical value (assuming twos-complement
* arithmetic). This is what we want: all legal negative values
* for clr will be greater than 255. */

/* Convert and clamp. */
result = (unsigned short)(short)(clr + 0.5);
if (result > 255) {
result = (clr < 0) ? 0 : 255;
if (result > max) {
result = (clr < 0) ? 0 : max;
}/* if */

return result;
}/* uchar_clamp*/

Expand All @@ -967,7 +975,9 @@ static inline void _gdScaleRow(gdImagePtr pSrc, unsigned int src_width, gdImage
b += contrib->ContribRow[x].Weights[left_channel] * (double)(gdTrueColorGetBlue(p_src_row[i]));
a += contrib->ContribRow[x].Weights[left_channel] * (double)(gdTrueColorGetAlpha(p_src_row[i]));
}
p_dst_row[x] = gdTrueColorAlpha(uchar_clamp(r), uchar_clamp(g), uchar_clamp(b), uchar_clamp(a));
p_dst_row[x] = gdTrueColorAlpha(uchar_clamp(r, 0xFF), uchar_clamp(g, 0xFF),
uchar_clamp(b, 0xFF),
uchar_clamp(a, 0x7F)); /* alpha is 0..127 */
}
}

Expand Down Expand Up @@ -1014,7 +1024,9 @@ static inline void _gdScaleCol (gdImagePtr pSrc, unsigned int src_width, gdImag
b += contrib->ContribRow[y].Weights[i_iLeft] * (double)(gdTrueColorGetBlue(pCurSrc));
a += contrib->ContribRow[y].Weights[i_iLeft] * (double)(gdTrueColorGetAlpha(pCurSrc));
}
pRes->tpixels[y][uCol] = gdTrueColorAlpha(uchar_clamp(r), uchar_clamp(g), uchar_clamp(b), uchar_clamp(a));
pRes->tpixels[y][uCol] = gdTrueColorAlpha(uchar_clamp(r, 0xFF), uchar_clamp(g, 0xFF),
uchar_clamp(b, 0xFF),
uchar_clamp(a, 0x7F)); /* alpha is 0..127 */
}
}

Expand Down
15 changes: 15 additions & 0 deletions ext/gd/tests/gh16559.phpt
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
--TEST--
GH-16559 (UBSan abort in ext/gd/libgd/gd_interpolation.c:1007)
--EXTENSIONS--
gd
--FILE--
<?php
$input = imagecreatefrompng(__DIR__ . '/gh10614.png');
for ($angle = 0; $angle <= 270; $angle += 90) {
$output = imagerotate($input, $angle, 0);
}
var_dump(imagescale($output, -1, 64, IMG_BICUBIC));
?>
--EXPECT--
object(GdImage)#2 (0) {
}
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