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video: Harden calculation of SDL_surface pitch and size against overflow 

If the width is sufficiently ludicrous, then the calculated pitch or
the image size could conceivably be a signed integer overflow, which
is undefined behaviour. Calculate in the unsigned size_t domain, with
overflow checks.

Signed-off-by: Simon McVittie <smcv@collabora.com>
This commit is contained in:
Simon McVittie 2022-05-10 10:33:54 +01:00 committed by Sam Lantinga
parent 6606ab8b56
commit 8c9f7104e3
1 changed files with 28 additions and 13 deletions
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41
src/video/SDL_surface.c
View File

@ -33,22 +33,37 @@
SDL_COMPILE_TIME_ASSERT(surface_size_assumptions,
sizeof(int) == sizeof(Sint32) && sizeof(size_t) >= sizeof(Sint32));
SDL_COMPILE_TIME_ASSERT(can_indicate_overflow, SDL_SIZE_MAX > SDL_MAX_SINT32);
/* Public routines */
/*
* Calculate the pad-aligned scanline width of a surface
* Calculate the pad-aligned scanline width of a surface.
* Return SDL_SIZE_MAX on overflow.
*/
static Sint64
SDL_CalculatePitch(Uint32 format, int width)
static size_t
SDL_CalculatePitch(Uint32 format, size_t width)
{
Sint64 pitch;
size_t pitch;
if (SDL_ISPIXELFORMAT_FOURCC(format) || SDL_BITSPERPIXEL(format) >= 8) {
pitch = ((Sint64)width * SDL_BYTESPERPIXEL(format));
if (SDL_size_mul_overflow(width, SDL_BYTESPERPIXEL(format), &pitch)) {
return SDL_SIZE_MAX;
}
} else {
pitch = (((Sint64)width * SDL_BITSPERPIXEL(format)) + 7) / 8;
if (SDL_size_mul_overflow(width, SDL_BITSPERPIXEL(format), &pitch)) {
return SDL_SIZE_MAX;
}
if (SDL_size_add_overflow(pitch, 7, &pitch)) {
return SDL_SIZE_MAX;
}
pitch /= 8;
}
pitch = (pitch + 3) & ~3; /* 4-byte aligning for speed */
/* 4-byte aligning for speed */
if (SDL_size_add_overflow(pitch, 3, &pitch)) {
return SDL_SIZE_MAX;
}
pitch &= ~3;
return pitch;
}
@ -60,14 +75,14 @@ SDL_Surface *
SDL_CreateRGBSurfaceWithFormat(Uint32 flags, int width, int height, int depth,
Uint32 format)
{
Sint64 pitch;
size_t pitch;
SDL_Surface *surface;
/* The flags are no longer used, make the compiler happy */
(void)flags;
pitch = SDL_CalculatePitch(format, width);
if (pitch < 0 || pitch > SDL_MAX_SINT32) {
if (pitch > SDL_MAX_SINT32) {
/* Overflow... */
SDL_OutOfMemory();
return NULL;
@ -113,15 +128,15 @@ SDL_CreateRGBSurfaceWithFormat(Uint32 flags, int width, int height, int depth,
/* Get the pixels */
if (surface->w && surface->h) {
/* Assumptions checked in surface_size_assumptions assert above */
Sint64 size = ((Sint64)surface->h * surface->pitch);
if (size < 0 || size > SDL_MAX_SINT32) {
size_t size;
if (SDL_size_mul_overflow(surface->h, surface->pitch, &size)) {
/* Overflow... */
SDL_FreeSurface(surface);
SDL_OutOfMemory();
return NULL;
}
surface->pixels = SDL_SIMDAlloc((size_t)size);
surface->pixels = SDL_SIMDAlloc(size);
if (!surface->pixels) {
SDL_FreeSurface(surface);
SDL_OutOfMemory();
@ -129,7 +144,7 @@ SDL_CreateRGBSurfaceWithFormat(Uint32 flags, int width, int height, int depth,
}
surface->flags |= SDL_SIMD_ALIGNED;
/* This is important for bitmaps */
SDL_memset(surface->pixels, 0, surface->h * surface->pitch);
SDL_memset(surface->pixels, 0, size);
}
/* Allocate an empty mapping */