Fixed CVE-2019-7635 and bug 4498 - Heap-Buffer Overflow in Blit1to4 pertaining 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).
diff --git a/src/video/SDL_bmp.c b/src/video/SDL_bmp.c
index 5974414..c676cc0 100644
--- a/src/video/SDL_bmp.c
+++ b/src/video/SDL_bmp.c
@@ -246,6 +246,14 @@
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 @@
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. */
