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CVE-2019-7635: Reject BMP images with pixel colors out the palette
If a 1-, 4-, or 8-bit per pixel BMP image declares less used colors
than the palette offers an SDL_Surface with a palette of the indicated
number of used colors is created. If some of the image's pixel
refer to a color number higher then the maximal used colors, a subsequent
bliting operation on the surface will look up a color past a blit map
(that is based on the palette) memory. I.e. passing such SDL_Surface
to e.g. an SDL_DisplayFormat() function will result in a buffer overread in
a blit function.

This patch fixes it by validing each pixel's color to be less than the
maximal color number in the palette. A validation failure raises an
error from a SDL_LoadBMP_RW() function.

CVE-2019-7635
https://bugzilla.libsdl.org/show_bug.cgi?id=4498

Signed-off-by: Petr P?sa? <ppisar@redhat.com>
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ppisar committed Jun 11, 2019
1 parent c68e000 commit 32c57bf53b18dafb7298d6e9113632728e8fe1ba
Showing with 16 additions and 0 deletions.
  1. +16 −0 src/video/SDL_bmp.c
@@ -308,6 +308,12 @@ SDL_Surface * SDL_LoadBMP_RW (SDL_RWops *src, int freesrc)
}
*(bits+i) = (pixel>>shift);
pixel <<= ExpandBMP;
if ( bits[i] >= biClrUsed ) {
SDL_SetError(
"A BMP image contains a pixel with a color out of the palette");
was_error = SDL_TRUE;
goto done;
}
} }
break;

@@ -318,6 +324,16 @@ SDL_Surface * SDL_LoadBMP_RW (SDL_RWops *src, int freesrc)
was_error = SDL_TRUE;
goto done;
}
if ( 8 == biBitCount && palette && biClrUsed < (1 << biBitCount ) ) {
for ( i=0; i<surface->w; ++i ) {
if ( bits[i] >= biClrUsed ) {
SDL_SetError(
"A BMP image contains a pixel with a color out of the palette");
was_error = SDL_TRUE;
goto done;
}
}
}
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
/* Byte-swap the pixels if needed. Note that the 24bpp
case has already been taken care of above. */

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