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Fixed CVE-2019-7635 and bug 4498 - Heap-Buffer Overflow in Blit1to4 p…

…ertaining to SDL_blit_1.c

Petr Pisar

The root cause is that the POC BMP file declares 3 colors used and 4 bpp palette, but pixel at line 28 and column 1 (counted from 0) has color number 3. Then when the image loaded into a surface is passed to SDL_DisplayFormat(), in order to convert it to a video format, a used bliting function looks up a color number 3 in a 3-element long color bliting map. (The map obviously has the same number entries as the surface format has colors.)

Proper fix should refuse broken BMP images that have a pixel with a color index higher than declared number of "used" colors. Possibly more advanced fix could try to relocate the out-of-range color index into a vacant index (if such exists).
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slouken committed Mar 17, 2019
1 parent 0f148eb commit 8bc59f87ecb8d7cd1e47b8a6c2c30d9c58ecf7a7
Showing with 24 additions and 3 deletions.
  1. +24 −3 src/video/SDL_bmp.c
@@ -246,6 +246,14 @@ SDL_LoadBMP_RW(SDL_RWops * src, int freesrc)
ExpandBMP = biBitCount;
biBitCount = 8;
break;
case 2:
case 3:
case 5:
case 6:
case 7:
SDL_SetError("%d-bpp BMP images are not supported", biBitCount);
was_error = SDL_TRUE;
goto done;
default:
ExpandBMP = 0;
break;
@@ -398,19 +406,32 @@ SDL_LoadBMP_RW(SDL_RWops * src, int freesrc)
goto done;
}
}
*(bits + i) = (pixel >> shift);
bits[i] = (pixel >> shift);
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;
}
pixel <<= ExpandBMP;
}
}
break;

default:
if (SDL_RWread(src, bits, 1, surface->pitch)
!= surface->pitch) {
if (SDL_RWread(src, bits, 1, surface->pitch) != surface->pitch) {
SDL_Error(SDL_EFREAD);
was_error = SDL_TRUE;
goto done;
}
if (biBitCount == 8 && 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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