calloc: Use calloc() at most places

This modifies most of the places we do some form of:

  X = malloc(Y * Z);

to use calloc(Y, Z) instead.

Among other issues, this fixes:
  - allocation of integer overflow in grub_png_decode_image_header()
    reported by Chris Coulson,
  - allocation of integer overflow in luks_recover_key()
    reported by Chris Coulson,
  - allocation of integer overflow in grub_lvm_detect()
    reported by Chris Coulson.

Fixes: CVE-2020-14308

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

util/grub-install.c

@@ -634,7 +634,7 @@ device_map_check_duplicates (const char *dev_map)
   if (! fp)
     return;
 
-  d = xmalloc (alloced * sizeof (d[0]));
+  d = xcalloc (alloced, sizeof (d[0]));
 
   while (fgets (buf, sizeof (buf), fp))
     {
@@ -1268,7 +1268,7 @@ main (int argc, char *argv[])
       ndev++;
     }
 
-  grub_drives = xmalloc (sizeof (grub_drives[0]) * (ndev + 1)); 
+  grub_drives = xcalloc (ndev + 1, sizeof (grub_drives[0]));
 
   for (curdev = grub_devices, curdrive = grub_drives; *curdev; curdev++,
        curdrive++)