staging/lustre/llite: Only kill SGID/SUID bits

Check that attr mode is valid before using it when determining if to
clear SGID and SUID bits in ll_setattr.
Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-on: http://review.whamcloud.com/10153
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4924Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/llite_lib.c

@@ -1537,12 +1537,14 @@ int ll_setattr(struct dentry *de, struct iattr *attr)
 	      !(attr->ia_mode & S_ISGID))))
 		attr->ia_valid |= ATTR_FORCE;
 
-	if ((mode & S_ISUID) &&
+	if ((attr->ia_valid & ATTR_MODE) &&
+	    (mode & S_ISUID) &&
 	    !(attr->ia_mode & S_ISUID) &&
 	    !(attr->ia_valid & ATTR_KILL_SUID))
 		attr->ia_valid |= ATTR_KILL_SUID;
 
-	if (((mode & (S_ISGID|S_IXGRP)) == (S_ISGID|S_IXGRP)) &&
+	if ((attr->ia_valid & ATTR_MODE) &&
+	    ((mode & (S_ISGID|S_IXGRP)) == (S_ISGID|S_IXGRP)) &&
 	    !(attr->ia_mode & S_ISGID) &&
 	    !(attr->ia_valid & ATTR_KILL_SGID))
 		attr->ia_valid |= ATTR_KILL_SGID;