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Support -D_FORTIFY_SOURCE=3 by using __builtin_dynamic_object_size.

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As explained in the issue, -D_FORTIFY_SOURCE=3 requires usage
of __builtin_dynamic_object_size in MALLOC_SIZEOF_SAFE macro.

Fixes: #22801
This commit is contained in:
Martin Liska 2022-03-31 10:27:45 +02:00 committed by Yu Watanabe
parent f887eab1da
commit 0bd292567a
1 changed files with 13 additions and 3 deletions
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16
src/basic/alloc-util.h
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@ -174,13 +174,23 @@ void* greedy_realloc0(void **p, size_t need, size_t size);
* is compatible with _FORTIFY_SOURCES. If _FORTIFY_SOURCES is used many memory operations will take the
* object size as returned by __builtin_object_size() into account. Hence, let's return the smaller size of
* malloc_usable_size() and __builtin_object_size() here, so that we definitely operate in safe territory by
* both the compiler's and libc's standards. Note that __builtin_object_size() evaluates to SIZE_MAX if the
* size cannot be determined, hence the MIN() expression should be safe with dynamically sized memory,
* too. Moreover, when NULL is passed malloc_usable_size() is documented to return zero, and
* both the compiler's and libc's standards. Note that _FORTIFY_SOURCES=3 handles also dynamically allocated
* objects and thus it's safer using __builtin_dynamic_object_size if _FORTIFY_SOURCES=3 is used (#22801).
* Moreover, when NULL is passed malloc_usable_size() is documented to return zero, and
* __builtin_object_size() returns SIZE_MAX too, hence we also return a sensible value of 0 in this corner
* case. */
#if defined __has_builtin
# if __has_builtin(__builtin_dynamic_object_size)
# define MALLOC_SIZEOF_SAFE(x) \
MIN(malloc_usable_size(x), __builtin_dynamic_object_size(x, 0))
# endif
#endif
#ifndef MALLOC_SIZEOF_SAFE
#define MALLOC_SIZEOF_SAFE(x) \
MIN(malloc_usable_size(x), __builtin_object_size(x, 0))
#endif
/* Inspired by ELEMENTSOF() but operates on malloc()'ed memory areas: typesafely returns the number of items
* that fit into the specified memory block */