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stdinc: Add overflow-checking add and multiply for size_t

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This can be used to check whether untrusted sizes would cause overflow
when used to calculate how much memory is needed.

Signed-off-by: Simon McVittie <smcv@collabora.com>
This commit is contained in:
Simon McVittie 2022-05-09 14:36:27 +01:00 committed by Sam Lantinga
parent 6e6e425e23
commit f661654fad
1 changed files with 60 additions and 0 deletions
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60
include/SDL_stdinc.h
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@ -115,6 +115,12 @@ char *alloca();
# endif
#endif
#ifdef SIZE_MAX
# define SDL_SIZE_MAX SIZE_MAX
#else
# define SDL_SIZE_MAX ((size_t) -1)
#endif
/**
* Check if the compiler supports a given builtin.
* Supported by virtually all clang versions and recent gcc. Use this
@ -728,6 +734,60 @@ SDL_FORCE_INLINE void *SDL_memcpy4(SDL_OUT_BYTECAP(dwords*4) void *dst, SDL_IN_B
return SDL_memcpy(dst, src, dwords * 4);
}
/**
* If a * b would overflow, return -1. Otherwise store a * b via ret
* and return 0.
*
* \since This function is available since SDL 2.24.0.
*/
SDL_FORCE_INLINE int SDL_size_mul_overflow (size_t a,
size_t b,
size_t *ret)
{
if (a != 0 && b > SDL_SIZE_MAX / a) {
return -1;
}
*ret = a * b;
return 0;
}
#if _SDL_HAS_BUILTIN(__builtin_mul_overflow)
SDL_FORCE_INLINE int _SDL_size_mul_overflow_builtin (size_t a,
size_t b,
size_t *ret)
{
return __builtin_mul_overflow(a, b, ret) == 0 ? 0 : -1;
}
#define SDL_size_mul_overflow(a, b, ret) (_SDL_size_mul_overflow_builtin(a, b, ret))
#endif
/**
* If a + b would overflow, return -1. Otherwise store a + b via ret
* and return 0.
*
* \since This function is available since SDL 2.24.0.
*/
SDL_FORCE_INLINE int SDL_size_add_overflow (size_t a,
size_t b,
size_t *ret)
{
if (b > SDL_SIZE_MAX - a) {
return -1;
}
*ret = a + b;
return 0;
}
#if _SDL_HAS_BUILTIN(__builtin_add_overflow)
SDL_FORCE_INLINE int _SDL_size_add_overflow_builtin (size_t a,
size_t b,
size_t *ret)
{
return __builtin_add_overflow(a, b, ret) == 0 ? 0 : -1;
}
#define SDL_size_add_overflow(a, b, ret) (_SDL_size_add_overflow_builtin(a, b, ret))
#endif
/* Ends C function definitions when using C++ */
#ifdef __cplusplus
}