malloc: make malloc fail with requests larger than PTRDIFF_MAX (BZ#23741)

As discussed previously on libc-alpha [1], this patch follows up the idea
and add both the __attribute_alloc_size__ on malloc functions (malloc,
calloc, realloc, reallocarray, valloc, pvalloc, and memalign) and limit
maximum requested allocation size to up PTRDIFF_MAX (taking into
consideration internal padding and alignment).

This aligns glibc with gcc expected size defined by default warning
-Walloc-size-larger-than value which warns for allocation larger than
PTRDIFF_MAX.  It also aligns with gcc expectation regarding libc and
expected size, such as described in PR#67999 [2] and previously discussed
ISO C11 issues [3] on libc-alpha.

From the RFC thread [4] and previous discussion, it seems that consensus
is only to limit such requested size for malloc functions, not the system
allocation one (mmap, sbrk, etc.).

The implementation changes checked_request2size to check for both overflow
and maximum object size up to PTRDIFF_MAX. No additional checks are done
on sysmalloc, so it can still issue mmap with values larger than
PTRDIFF_T depending on the requested size.

The __attribute_alloc_size__ is for functions that return a pointer only,
which means it cannot be applied to posix_memalign (see remarks in GCC
PR#87683 [5]). The runtimes checks to limit maximum requested allocation
size does applies to posix_memalign.

Checked on x86_64-linux-gnu and i686-linux-gnu.

[1] https://sourceware.org/ml/libc-alpha/2018-11/msg00223.html
[2] https://gcc.gnu.org/bugzilla//show_bug.cgi?id=67999
[3] https://sourceware.org/ml/libc-alpha/2011-12/msg00066.html
[4] https://sourceware.org/ml/libc-alpha/2018-11/msg00224.html
[5] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87683

	[BZ #23741]
	* malloc/hooks.c (malloc_check, realloc_check): Use
	__builtin_add_overflow on overflow check and adapt to
	checked_request2size change.
	* malloc/malloc.c (__libc_malloc, __libc_realloc, _mid_memalign,
	__libc_pvalloc, __libc_calloc, _int_memalign): Limit maximum
	allocation size to PTRDIFF_MAX.
	(REQUEST_OUT_OF_RANGE): Remove macro.
	(checked_request2size): Change to inline function and limit maximum
	requested size to PTRDIFF_MAX.
	(__libc_malloc, __libc_realloc, _int_malloc, _int_memalign): Limit
	maximum allocation size to PTRDIFF_MAX.
	(_mid_memalign): Use _int_memalign call for overflow check.
	(__libc_pvalloc): Use __builtin_add_overflow on overflow check.
	(__libc_calloc): Use __builtin_mul_overflow for overflow check and
	limit maximum requested size to PTRDIFF_MAX.
	* malloc/malloc.h (malloc, calloc, realloc, reallocarray, memalign,
	valloc, pvalloc): Add __attribute_alloc_size__.
	* stdlib/stdlib.h (malloc, realloc, reallocarray, valloc): Likewise.
	* malloc/tst-malloc-too-large.c (do_test): Add check for allocation
	larger than PTRDIFF_MAX.
	* malloc/tst-memalign.c (do_test): Disable -Walloc-size-larger-than=
	around tests of malloc with negative sizes.
	* malloc/tst-posix_memalign.c (do_test): Likewise.
	* malloc/tst-pvalloc.c (do_test): Likewise.
	* malloc/tst-valloc.c (do_test): Likewise.
	* malloc/tst-reallocarray.c (do_test): Replace call to reallocarray
	with resulting size allocation larger than PTRDIFF_MAX with
	reallocarray_nowarn.
	(reallocarray_nowarn): New function.
	* NEWS: Mention the malloc function semantic change.

malloc/malloc.h

@@ -35,11 +35,12 @@
 __BEGIN_DECLS
 
 /* Allocate SIZE bytes of memory.  */
-extern void *malloc (size_t __size) __THROW __attribute_malloc__ __wur;
+extern void *malloc (size_t __size) __THROW __attribute_malloc__
+     __attribute_alloc_size__ ((1)) __wur;
 
 /* Allocate NMEMB elements of SIZE bytes each, all initialized to 0.  */
 extern void *calloc (size_t __nmemb, size_t __size)
-__THROW __attribute_malloc__ __wur;
+__THROW __attribute_malloc__ __attribute_alloc_size__ ((1, 2)) __wur;
 
 /* Re-allocate the previously allocated block in __ptr, making the new
    block SIZE bytes long.  */
@@ -47,7 +48,7 @@ __THROW __attribute_malloc__ __wur;
    the same pointer that was passed to it, aliasing needs to be allowed
    between objects pointed by the old and new pointers.  */
 extern void *realloc (void *__ptr, size_t __size)
-__THROW __attribute_warn_unused_result__;
+__THROW __attribute_warn_unused_result__ __attribute_alloc_size__ ((2));
 
 /* Re-allocate the previously allocated block in PTR, making the new
    block large enough for NMEMB elements of SIZE bytes each.  */
@@ -55,21 +56,23 @@ __THROW __attribute_warn_unused_result__;
    the same pointer that was passed to it, aliasing needs to be allowed
    between objects pointed by the old and new pointers.  */
 extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
-__THROW __attribute_warn_unused_result__;
+__THROW __attribute_warn_unused_result__ __attribute_alloc_size__ ((2, 3));
 
 /* Free a block allocated by `malloc', `realloc' or `calloc'.  */
 extern void free (void *__ptr) __THROW;
 
 /* Allocate SIZE bytes allocated to ALIGNMENT bytes.  */
 extern void *memalign (size_t __alignment, size_t __size)
-__THROW __attribute_malloc__ __wur;
+__THROW __attribute_malloc__ __attribute_alloc_size__ ((2)) __wur;
 
 /* Allocate SIZE bytes on a page boundary.  */
-extern void *valloc (size_t __size) __THROW __attribute_malloc__ __wur;
+extern void *valloc (size_t __size) __THROW __attribute_malloc__
+     __attribute_alloc_size__ ((1)) __wur;
 
 /* Equivalent to valloc(minimum-page-that-holds(n)), that is, round up
    __size to nearest pagesize. */
-extern void *pvalloc (size_t __size) __THROW __attribute_malloc__ __wur;
+extern void *pvalloc (size_t __size) __THROW __attribute_malloc__
+     __attribute_alloc_size__ ((1)) __wur;
 
 /* Underlying allocation function; successive calls should return
    contiguous pieces of memory.  */