NFS: nfs_setattr_update_inode() should clear the suid/sgid bits

When we do a 'chown' or 'chgrp', the server will clear the suid/sgid
bits. Ensure that we mirror that in nfs_setattr_update_inode().
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/inode.c

@@ -636,8 +636,7 @@ nfs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 	}
 
 	/* Optimization: if the end result is no change, don't RPC */
-	attr->ia_valid &= NFS_VALID_ATTRS;
-	if ((attr->ia_valid & ~(ATTR_FILE|ATTR_OPEN)) == 0)
+	if (((attr->ia_valid & NFS_VALID_ATTRS) & ~(ATTR_FILE|ATTR_OPEN)) == 0)
 		return 0;
 
 	trace_nfs_setattr_enter(inode);
@@ -719,6 +718,13 @@ void nfs_setattr_update_inode(struct inode *inode, struct iattr *attr,
 	}
 	if ((attr->ia_valid & (ATTR_MODE|ATTR_UID|ATTR_GID)) != 0) {
 		NFS_I(inode)->cache_validity &= ~NFS_INO_INVALID_CTIME;
+		if ((attr->ia_valid & ATTR_KILL_SUID) != 0 &&
+		    inode->i_mode & S_ISUID)
+			inode->i_mode &= ~S_ISUID;
+		if ((attr->ia_valid & ATTR_KILL_SGID) != 0 &&
+		    (inode->i_mode & (S_ISGID | S_IXGRP)) ==
+		     (S_ISGID | S_IXGRP))
+			inode->i_mode &= ~S_ISGID;
 		if ((attr->ia_valid & ATTR_MODE) != 0) {
 			int mode = attr->ia_mode & S_IALLUGO;
 			mode |= inode->i_mode & ~S_IALLUGO;