Mercurial > gnulib
changeset 38240:f9dafd51172a
xalloc-oversized: check for PTRDIFF_MAX too
This avoids undefined behavior when subtracting pointers to
objects containing more than PTRDIFF_MAX bytes.
* lib/xalloc-oversized.h (__xalloc_oversized, xalloc_oversized):
Also return 1 if the result would exceed PTRDIFF_MAX>
* modules/xalloc-oversized (Depends-on):
Add stdint.
| author | Paul Eggert <eggert@cs.ucla.edu> |
|---|---|
| date | Wed, 14 Dec 2016 17:09:04 -0800 |
| parents | ed050cfccdb2 |
| children | 909a440ad711 |
| files | ChangeLog lib/xalloc-oversized.h modules/xalloc-oversized |
| diffstat | 3 files changed, 29 insertions(+), 15 deletions(-) [+] |
line wrap: on
line diff
--- a/ChangeLog Wed Dec 14 15:11:28 2016 -0800 +++ b/ChangeLog Wed Dec 14 17:09:04 2016 -0800 @@ -1,5 +1,13 @@ 2016-12-14 Paul Eggert <eggert@cs.ucla.edu> + xalloc-oversized: check for PTRDIFF_MAX too + This avoids undefined behavior when subtracting pointers to + objects containing more than PTRDIFF_MAX bytes. + * lib/xalloc-oversized.h (__xalloc_oversized, xalloc_oversized): + Also return 1 if the result would exceed PTRDIFF_MAX> + * modules/xalloc-oversized (Depends-on): + Add stdint. + dfa: fix glitches in previous commit Sorry, I don't know how I managed to commit the wrong version. * lib/dfa.c (MIN): Move up.
--- a/lib/xalloc-oversized.h Wed Dec 14 15:11:28 2016 -0800 +++ b/lib/xalloc-oversized.h Wed Dec 14 17:09:04 2016 -0800 @@ -19,32 +19,36 @@ #define XALLOC_OVERSIZED_H_ #include <stddef.h> +#include <stdint.h> /* Default for (non-Clang) compilers that lack __has_builtin. */ #ifndef __has_builtin # define __has_builtin(x) 0 #endif -/* True if N * S would overflow in a size calculation. +/* True if N * S would overflow in a size_t calculation, + or would generate a value larger than PTRDIFF_MAX. This expands to a constant expression if N and S are both constants. By gnulib convention, SIZE_MAX represents overflow in size - calculations, so the conservative dividend to use here is - SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value. - However, malloc (SIZE_MAX) fails on all known hosts where - sizeof (ptrdiff_t) <= sizeof (size_t), so do not bother to test for - exactly-SIZE_MAX allocations on such hosts; this avoids a test and - branch when S is known to be 1. */ + calculations, so the conservative size_t-based dividend to use here + is SIZE_MAX - 1. */ #define __xalloc_oversized(n, s) \ - ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n)) - + ((size_t) (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) < (n)) -/* Return 1 if an array of N objects, each of size S, cannot exist due - to size arithmetic overflow. S must be positive and N must be - nonnegative. This is a macro, not a function, so that it - works correctly even when SIZE_MAX < N. */ +#if PTRDIFF_MAX < SIZE_MAX +typedef ptrdiff_t __xalloc_count_type; +#else +typedef size_t __xalloc_count_type; +#endif + +/* Return 1 if an array of N objects, each of size S, cannot exist + reliably due to size or ptrdiff_t arithmetic overflow. S must be + positive and N must be nonnegative. This is a macro, not a + function, so that it works correctly even when SIZE_MAX < N. */ #if 7 <= __GNUC__ || __has_builtin (__builtin_add_overflow_p) -# define xalloc_oversized(n, s) __builtin_mul_overflow_p (n, s, (size_t) 1) +# define xalloc_oversized(n, s) \ + __builtin_mul_overflow_p (n, s, (__xalloc_count_type) 1) #elif ((5 <= __GNUC__ \ || (__has_builtin (__builtin_mul_overflow) \ && __has_builtin (__builtin_constant_p))) \ @@ -52,7 +56,8 @@ # define xalloc_oversized(n, s) \ (__builtin_constant_p (n) && __builtin_constant_p (s) \ ? __xalloc_oversized (n, s) \ - : ({ size_t __xalloc_size; __builtin_mul_overflow (n, s, &__xalloc_size); })) + : ({ __xalloc_count_type __xalloc_count; \ + __builtin_mul_overflow (n, s, &__xalloc_count); })) /* Other compilers use integer division; this may be slower but is more portable. */