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>

grub-core/fs/affs.c

@@ -301,7 +301,7 @@ grub_affs_read_symlink (grub_fshelp_node_t node)
       return 0;
     }
   latin1[symlink_size] = 0;
-  utf8 = grub_malloc (symlink_size * GRUB_MAX_UTF8_PER_LATIN1 + 1);
+  utf8 = grub_calloc (GRUB_MAX_UTF8_PER_LATIN1 + 1, symlink_size);
   if (!utf8)
     {
       grub_free (latin1);
@@ -422,7 +422,7 @@ grub_affs_iterate_dir (grub_fshelp_node_t dir,
 	return 1;
     }
 
-  hashtable = grub_zalloc (data->htsize * sizeof (*hashtable));
+  hashtable = grub_calloc (data->htsize, sizeof (*hashtable));
   if (!hashtable)
     return 1;
 
@@ -628,7 +628,7 @@ grub_affs_label (grub_device_t device, char **label)
       len = file.namelen;
       if (len > sizeof (file.name))
 	len = sizeof (file.name);
-      *label = grub_malloc (len * GRUB_MAX_UTF8_PER_LATIN1 + 1);
+      *label = grub_calloc (GRUB_MAX_UTF8_PER_LATIN1 + 1, len);
       if (*label)
 	*grub_latin1_to_utf8 ((grub_uint8_t *) *label, file.name, len) = '\0';
     }