From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [Patch net] socket: close race condition between sock_close() and sockfs_setattr() Date: Thu, 7 Jun 2018 23:04:47 +0100 Message-ID: <20180607220446.GX30522@ZenIV.linux.org.uk> References: <20180607203949.16945-1-xiyou.wangcong@gmail.com> <20180607212631.GW30522@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Linux Kernel Network Developers , shankarapailoor , Tetsuo Handa , Lorenzo Colitti To: Cong Wang Return-path: Received: from zeniv.linux.org.uk ([195.92.253.2]:56836 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751752AbeFGWEs (ORCPT ); Thu, 7 Jun 2018 18:04:48 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Jun 07, 2018 at 02:45:58PM -0700, Cong Wang wrote: > On Thu, Jun 7, 2018 at 2:26 PM, Al Viro wrote: > > On Thu, Jun 07, 2018 at 01:39:49PM -0700, Cong Wang wrote: > >> fchownat() doesn't even hold refcnt of fd until it figures out > >> fd is really needed (otherwise is ignored) and releases it after > >> it resolves the path. This means sock_close() could race with > >> sockfs_setattr(), which leads to a NULL pointer dereference > >> since typically we set sock->sk to NULL in ->release(). > >> > >> As pointed out by Al, this is unique to sockfs. So we can fix this > >> in socket layer by acquiring inode_lock in sock_close() and > >> checking against NULL in sockfs_setattr(). > > > > That looks like a massive overkill - it's way heavier than it should be. > > I don't see any other quick way to fix this. My initial thought is > to keep that refcnt until path_put(), apparently you don't like it > either. You do realize that the same ->setattr() can be called by way of chown() on /proc/self/fd/, right? What would you do there - bump refcount on that struct file when traversing that symlink and hold it past the end of pathname resolution, until... what exactly?