bug 76041

• behavior: segmentation fault

• description: draw anti-alised line on a palette image resource

• sketch:

  • php_gd_gdImageCreate at ext/gd/libgd/gd.c:213

    im->tpixels = 0;

    line 2 $im=imagecreate(100,100); in poc.php is to create a new palette based image that doesn't support truecolor.

  • php_gd_gdImageSetAntiAliased at ext/gd/libgd/gd.c:2826

    im->AA = 1;

    line 3 imageantialias($im,true); activate the fast drawing antialiased methods for lines and wired polygons, which is a feature that works only with truecolor images.

  • zif_imageline at ext/gd/gd.c:3191

    if (im->AA) {
        gdImageSetAntiAliased(im, col);
        col = gdAntiAliased;
    }
    gdImageLine(im, x1, y1, x2, y2, col);

    • php_gd_gdImageLine at ext/gd/libgd/gd.c:1053

      if (color == gdAntiAliased) {
          /*
              gdAntiAliased passed as color: use the much faster, much cheaper
              and equally attractive gdImageAALine implementation. That
              clips too, so don't clip twice.
              */
          gdImageAALine(im, x1, y1, x2, y2, im->AA_color);
          return;
      }

      • php_gd_gdImageAALine at ext/gd/libgd/gd.c:1270

        gdImageSetAAPixelColor(im, x, y + 1, col, (~frac >> 8) & 0xFF);

        Set truecolor for antialised line pixel by pixel.

        • gdImageSetAAPixelColor at ext/gd/libgd/gd.c:1230

          im->tpixels[y][x]=gdTrueColorAlpha(dr, dg, db, gdAlphaOpaque);

          However, $im is a palette based image, which means it doesn't have truecolor pixels. Recal im->tpixels = 0, segmentation fault.

• patch: check if the image is of true color before draw anti-alised lines