apparmor: fix long path failure due to disconnected path

BugLink: http://bugs.launchpad.net/bugs/955892

All failures from __d_path where being treated as disconnected paths,
however __d_path can also fail when the generated pathname is too long.

The initial ENAMETOOLONG error was being lost, and ENAMETOOLONG was only
returned if the subsequent dentry_path call resulted in that error.  Other
wise if the path was split across a mount point such that the dentry_path
fit within the buffer when the __d_path did not the failure was treated
as a disconnected path.
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/path.c

@@ -94,6 +94,8 @@ static int d_namespace_path(struct path *path, char *buf, int buflen,
 	 * be returned.
 	 */
 	if (!res || IS_ERR(res)) {
+		if (PTR_ERR(res) == -ENAMETOOLONG)
+			return -ENAMETOOLONG;
 		connected = 0;
 		res = dentry_path_raw(path->dentry, buf, buflen);
 		if (IS_ERR(res)) {