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fix: Prevent overflow in chromaticity calculations

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In `png_xy_from_XYZ` X+Y+Z was calculated without checking for overflow.
This fixes that by moving the correct code from `png_XYZ_normalize` into
a static function which is now used from `png_xy_from_XYZ`.

Reviewed-by: Cosmin Truta <ctruta@gmail.com>
Signed-off-by: John Bowler <jbowler@acm.org>
Signed-off-by: Cosmin Truta <ctruta@gmail.com>
This commit is contained in:
John Bowler 2024-09-11 12:27:03 -07:00 committed by Cosmin Truta
parent 8cc22a8c15
commit 5a7e87fc04
1 changed files with 46 additions and 25 deletions
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71
png.c
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@ -1203,6 +1203,24 @@ png_colorspace_sync(png_const_structrp png_ptr, png_inforp info_ptr)
#endif /* GAMMA */
#ifdef PNG_COLORSPACE_SUPPORTED
static int
png_safe_add(png_int_32 *addend0_and_result, png_int_32 addend1,
png_int_32 addend2) {
/* Safely add three integers. Returns 0 on success, 1 on overlow.
* IMPLEMENTATION NOTE: ANSI requires signed overflow not to occur, therefore
* relying on addition of two positive values producing a negative one is not
* safe.
*/
int addend0 = *addend0_and_result;
if (0x7fffffff - addend0 < addend1)
return 1;
addend0 += addend1;
if (0x7fffffff - addend1 < addend2)
return 1;
*addend0_and_result = addend0 + addend2;
return 0;
}
/* Added at libpng-1.5.5 to support read and write of true CIEXYZ values for
* cHRM, as opposed to using chromaticities. These internal APIs return
* non-zero on a parameter error. The X, Y and Z values are required to be
@ -1211,38 +1229,52 @@ png_colorspace_sync(png_const_structrp png_ptr, png_inforp info_ptr)
static int
png_xy_from_XYZ(png_xy *xy, const png_XYZ *XYZ)
{
png_int_32 d, dwhite, whiteX, whiteY;
png_int_32 d, dred, dgreen, dwhite, whiteX, whiteY;
d = XYZ->red_X + XYZ->red_Y + XYZ->red_Z;
/* 'd' in each of the blocks below is just X+Y+Z for each component,
* x, y and z are X,Y,Z/(X+Y+Z).
*/
d = XYZ->red_X;
if (png_safe_add(&d, XYZ->red_Y, XYZ->red_Z))
return 1;
if (png_muldiv(&xy->redx, XYZ->red_X, PNG_FP_1, d) == 0)
return 1;
if (png_muldiv(&xy->redy, XYZ->red_Y, PNG_FP_1, d) == 0)
return 1;
dwhite = d;
dred = d;
whiteX = XYZ->red_X;
whiteY = XYZ->red_Y;
d = XYZ->green_X + XYZ->green_Y + XYZ->green_Z;
d = XYZ->green_X;
if (png_safe_add(&d, XYZ->green_Y, XYZ->green_Z))
return 1;
if (png_muldiv(&xy->greenx, XYZ->green_X, PNG_FP_1, d) == 0)
return 1;
if (png_muldiv(&xy->greeny, XYZ->green_Y, PNG_FP_1, d) == 0)
return 1;
dwhite += d;
dgreen = d;
whiteX += XYZ->green_X;
whiteY += XYZ->green_Y;
d = XYZ->blue_X + XYZ->blue_Y + XYZ->blue_Z;
d = XYZ->blue_X;
if (png_safe_add(&d, XYZ->blue_Y, XYZ->blue_Z))
return 1;
if (png_muldiv(&xy->bluex, XYZ->blue_X, PNG_FP_1, d) == 0)
return 1;
if (png_muldiv(&xy->bluey, XYZ->blue_Y, PNG_FP_1, d) == 0)
return 1;
dwhite += d;
whiteX += XYZ->blue_X;
whiteY += XYZ->blue_Y;
/* The reference white is simply the sum of the end-point (X,Y,Z) vectors,
* thus:
/* The reference white is simply the sum of the end-point (X,Y,Z) vectors so
* the fillowing calculates (X+Y+Z) of the reference white (media white,
* encoding white) itself:
*/
if (png_safe_add(&d, dred, dgreen))
return 1;
dwhite = d;
if (png_muldiv(&xy->whitex, whiteX, PNG_FP_1, dwhite) == 0)
return 1;
if (png_muldiv(&xy->whitey, whiteY, PNG_FP_1, dwhite) == 0)
@ -1506,25 +1538,14 @@ png_XYZ_from_xy(png_XYZ *XYZ, const png_xy *xy)
static int
png_XYZ_normalize(png_XYZ *XYZ)
{
png_int_32 Y;
png_int_32 Y, Ytemp;
if (XYZ->red_Y < 0 || XYZ->green_Y < 0 || XYZ->blue_Y < 0 ||
XYZ->red_X < 0 || XYZ->green_X < 0 || XYZ->blue_X < 0 ||
XYZ->red_Z < 0 || XYZ->green_Z < 0 || XYZ->blue_Z < 0)
/* Normalize by scaling so the sum of the end-point Y values is PNG_FP_1. */
Ytemp = XYZ->red_Y;
if (png_safe_add(&Ytemp, XYZ->green_Y, XYZ->blue_Y))
return 1;
/* Normalize by scaling so the sum of the end-point Y values is PNG_FP_1.
* IMPLEMENTATION NOTE: ANSI requires signed overflow not to occur, therefore
* relying on addition of two positive values producing a negative one is not
* safe.
*/
Y = XYZ->red_Y;
if (0x7fffffff - Y < XYZ->green_X)
return 1;
Y += XYZ->green_Y;
if (0x7fffffff - Y < XYZ->blue_X)
return 1;
Y += XYZ->blue_Y;
Y = Ytemp;
if (Y != PNG_FP_1)
{