Add reallocarray function

The reallocarray function is an extension from OpenBSD.  It is an
integer-overflow-safe replacement for realloc(p, X*Y) and
malloc(X*Y) (realloc(NULL, X*Y)).  It can therefore help in preventing
certain security issues in code.

This is an updated version of a patch originally submitted by Rüdiger
Sonderfeld in May 2014 [1].

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

[1] <https://sourceware.org/ml/libc-alpha/2014-05/msg00481.html>.

2017-05-30  Dennis Wölfing  <denniswoelfing@gmx.de>
            Rüdiger Sonderfeld  <ruediger@c-plusplus.de>

	* include/stdlib.h (__libc_reallocarray): New declaration.
	* malloc/Makefile (routines): Add reallocarray.
	(tests): Add tst-reallocarray.c.
	* malloc/Versions: Add reallocarray and __libc_reallocarray.
	* malloc/malloc-internal.h (check_mul_overflow_size_t): New inline
	function.
	* malloc/malloc.h (reallocarray): New declaration.
	* stdlib/stdlib.h (reallocarray): Likewise.
	* malloc/reallocarray.c: New file.
	* malloc/tst-reallocarray.c: New test file.
	* manual/memory.texi: Document reallocarray.
	* sysdeps/unix/sysv/linux/aarch64/libc.abilist: Add reallocarray.
	* sysdeps/unix/sysv/linux/alpha/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/arm/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/hppa/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/i386/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/ia64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/nios2/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sh/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/tilepro/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/libc.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist: Likewise.

1 files changed, 11 insertions, 0 deletions

diff --git a/stdlib/stdlib.h b/stdlib/stdlib.h
index 99125f2d23..428ca2ef68 100644
--- a/stdlib/stdlib.h
+++ b/stdlib/stdlib.h
@@ -422,6 +422,17 @@ extern void *calloc (size_t __nmemb, size_t __size)
    between objects pointed by the old and new pointers.  */
 extern void *realloc (void *__ptr, size_t __size)
      __THROW __attribute_warn_unused_result__;
+
+#ifdef __USE_GNU
+/* Re-allocate the previously allocated block in PTR, making the new
+   block large enough for NMEMB elements of SIZE bytes each.  */
+/* __attribute_malloc__ is not used, because if reallocarray returns
+   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__;
+#endif
+
 /* Free a block allocated by `malloc', `realloc' or `calloc'.  */
 extern void free (void *__ptr) __THROW;