Fixed bug 4536 - Heap-Buffer Overflow in SDL_GetRGB pertaining to SDL_pixels.c

Ozkan Sezer

As for the issue: This bmp reports bpp=0, therefore SDL_CalculatePitch()
returns pitch==0, which is then fed to SDL_malloc() (which is malloc())
and malloc(0) returns _something_ which is not NULL but not someting
that we expect..  Then testsprite.c:LoadSprite() accesses the pixels
as *(Uint8*)pixels which valrind reports as:

==15533== Invalid read of size 1
==15533==    at 0x8048C08: LoadSprite (testsprite.c:45)
==15533==    by 0x80492FC: main (testsprite.c:224)
==15533==  Address 0x449e588 is 0 bytes after a block of size 0 alloc'd
==15533==    at 0x40072B2: malloc (vg_replace_malloc.c:270)
==15533==    by 0x4045719: SDL_CreateRGBSurface (SDL_surface.c:126)
==15533==    by 0x40403C1: SDL_LoadBMP_RW (SDL_bmp.c:237)
==15533==    by 0x8048BB2: LoadSprite (testsprite.c:36)
==15533==    by 0x80492FC: main (testsprite.c:224)

Besides, valrind also reports this:
==15533== Conditional jump or move depends on uninitialised value(s)
==15533==    at 0x40403F3: SDL_LoadBMP_RW (SDL_bmp.c:247)
==15533==    by 0x8048BB2: LoadSprite (testsprite.c:36)
==15533==    by 0x80492FC: main (testsprite.c:224)


Easy/quick solution would be early-rejecting a bmp with 0 bpp from SDL_bmp.c:SDL_LoadBMP_RW()

src/video/SDL_bmp.c

@@ -331,6 +331,7 @@ SDL_LoadBMP_RW(SDL_RWops * src, int freesrc)
         ExpandBMP = biBitCount;
         biBitCount = 8;
         break;
+    case 0:
     case 2:
     case 3:
     case 5: