NFS: Don't clobber the attribute type in nfs_update_inode()

If the NFS_ATTR_FATTR_TYPE field isn't set in fattr->valid, then we should
not set the S_IFMT part of inode->i_mode.
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/inode.c

@@ -1261,8 +1261,10 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 
 	if (fattr->valid & NFS_ATTR_FATTR_MODE) {
 		if ((inode->i_mode & S_IALLUGO) != (fattr->mode & S_IALLUGO)) {
+			umode_t newmode = inode->i_mode & S_IFMT;
+			newmode |= fattr->mode & S_IALLUGO;
+			inode->i_mode = newmode;
 			invalid |= NFS_INO_INVALID_ATTR|NFS_INO_INVALID_ACCESS|NFS_INO_INVALID_ACL;
-			inode->i_mode = fattr->mode;
 		}
 	} else if (server->caps & NFS_CAP_MODE)
 		invalid |= save_cache_validity & (NFS_INO_INVALID_ATTR