calloc: Make sure we always have an overflow-checking calloc() available

This tries to make sure that everywhere in this source tree, we always have
an appropriate version of calloc() (i.e. grub_calloc(), xcalloc(), etc.)
available, and that they all safely check for overflow and return NULL when
it would occur.

Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/lib/libgcrypt_wrap/mem.c

@@ -4,6 +4,7 @@
 #include <grub/crypto.h>
 #include <grub/dl.h>
 #include <grub/env.h>
+#include <grub/safemath.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -36,7 +37,10 @@ void *
 gcry_xcalloc (size_t n, size_t m)
 {
   void *ret;
-  ret = grub_zalloc (n * m);
+  size_t sz;
+  if (grub_mul (n, m, &sz))
+    grub_fatal ("gcry_xcalloc would overflow");
+  ret = grub_zalloc (sz);
   if (!ret)
     grub_fatal ("gcry_xcalloc failed");
   return ret;
@@ -56,7 +60,10 @@ void *
 gcry_xcalloc_secure (size_t n, size_t m)
 {
   void *ret;
-  ret = grub_zalloc (n * m);
+  size_t sz;
+  if (grub_mul (n, m, &sz))
+    grub_fatal ("gcry_xcalloc would overflow");
+  ret = grub_zalloc (sz);
   if (!ret)
     grub_fatal ("gcry_xcalloc failed");
   return ret;