From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D78CC433DF for ; Wed, 5 Aug 2020 19:29:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4096D206F6 for ; Wed, 5 Aug 2020 19:29:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="gdQb9kf4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727789AbgHET21 (ORCPT ); Wed, 5 Aug 2020 15:28:27 -0400 Received: from linux.microsoft.com ([13.77.154.182]:49966 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728613AbgHERLb (ORCPT ); Wed, 5 Aug 2020 13:11:31 -0400 Received: from localhost.localdomain (c-73-172-233-15.hsd1.md.comcast.net [73.172.233.15]) by linux.microsoft.com (Postfix) with ESMTPSA id CA60120B4908; Wed, 5 Aug 2020 05:37:42 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com CA60120B4908 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1596631063; bh=JYxQh5HDRtdGXM5MNnERvMqtl0ye3vvdzDIHqIgr9iY=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=gdQb9kf4lUK5J+6cBCV7sBf3V3bJ87T2E/9NCIcqz7ORMCGIUKE4Zn/0UM5EViL3Q 9iD8bIlOgrgzGqXQzPAm8va9ajjVY990wyIU9Q7gK8Q9VZzOAEPfudn/QHm67jRexA VG0bllM2MBxyNaknlRu2BK6e+Th5cBen+1gOo+gU= Subject: Re: [RFC PATCH] selinux: move policy commit after updating selinuxfs To: Stephen Smalley , paul@paul-moore.com Cc: omosnace@redhat.com, selinux@vger.kernel.org References: <20200804135352.5650-1-stephen.smalley.work@gmail.com> <88c312b3-0abd-96ed-35c3-a80ab57a9fe3@linux.microsoft.com> <685a0fd4-d5a2-0cc8-4b9d-ad39cf916b16@gmail.com> From: Daniel Burgener Message-ID: Date: Wed, 5 Aug 2020 08:37:41 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <685a0fd4-d5a2-0cc8-4b9d-ad39cf916b16@gmail.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: selinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org On 8/5/20 8:35 AM, Stephen Smalley wrote: > On 8/4/20 4:51 PM, Daniel Burgener wrote: > >> On 8/4/20 9:53 AM, Stephen Smalley wrote: >>> With the refactoring of the policy load logic in the security >>> server from the previous change, it is now possible to split out >>> the committing of the new policy from security_load_policy() and >>> perform it only after successful updating of selinuxfs. Change >>> security_load_policy() to return the newly populated policy >>> data structures to the caller, export selinux_policy_commit() >>> for external callers, and introduce selinux_policy_cancel() to >>> provide a way to cancel the policy load in the event of an error >>> during updating of the selinuxfs directory tree.  Further, rework >>> the interfaces used by selinuxfs to get information from the policy >>> when creating the new directory tree to take and act upon the >>> new policy data structure rather than the current/active policy. >>> Update selinuxfs to use these updated and new interfaces. While >>> we are here, stop re-creating the policy_capabilities directory >>> on each policy load since it does not depend on the policy, and >>> stop trying to create the booleans and classes directories during >>> the initial creation of selinuxfs since no information is available >>> until first policy load. >>> >>> After this change, a failure while updating the booleans and class >>> directories will cause the entire policy load to be canceled, leaving >>> the original policy intact, and policy load notifications to userspace >>> will only happen after a successful completion of updating those >>> directories.  This does not (yet) provide full atomicity with respect >>> to the updating of the directory trees themselves. >> >> I have a patch series to perform the atomic updates very close to >> done, using vfs_rename with RENAME_EXCHANGE to update the directories >> out of tree and then swap them in as discussed earlier.  I've just >> been doing some final style cleanup before sending to the list.  I'll >> need to rebase on top of these changes of course.  I didn't touch any >> of the error recovery portions, so I hope my series will complement >> this patch nicely. > > Great, I was trying to ensure that we wouldn't conflict/overlap > significantly. > >>> This patch is relative to my previous one, >>> https://patchwork.kernel.org/patch/11698505/. Although this does >>> not ensure atomicity when updating the selinuxfs directoty tree, >>> I suspect it will solve Daniel's original bug because systemd/dbusd >>> won't get the policy load notifications until the kernel is done >>> updating selinuxfs and therefore won't try to re-read selinuxfs >>> in the middle of it (because libselinux caches the class/perm >>> mappings and only flushes on a reload). >> I agree with your suspicion that this will resolve the bug we've been >> seeing (although only as a result of changing the timing, as you >> point out).  Thanks for your work on this! > > If you can easily test that my patches resolve that bug for you, you > could add a Tested-by tag.  One caveat is that it sounds like I'll be > making one more change to the previous patch per Ondrej's request to > avoid taking the read lock around sidtab_convert(). Sounds good.  I will wait for your update, and then test this series. > >>>   @@ -563,15 +560,19 @@ static ssize_t sel_write_load(struct file >>> *file, const char __user *buf, >>>       if (copy_from_user(data, buf, count) != 0) >>>           goto out; >>>   -    length = security_load_policy(fsi->state, data, count); >>> +    length = security_load_policy(fsi->state, data, count, >>> &newpolicy); >>>       if (length) { >>>           pr_warn_ratelimited("SELinux: failed to load policy\n"); >>>           goto out; >>>       } >>>   -    length = sel_make_policy_nodes(fsi); >>> -    if (length) >>> +    length = sel_make_policy_nodes(fsi, newpolicy); >>> +    if (length) { >>> +        selinux_policy_cancel(fsi->state, newpolicy); >>>           goto out1; >> As things stand as of this patch, I think that this means that in the >> event of a failure in recreating the directories, that directory will >> be left unpopulated or partially populated.  We could even get in a >> state where the booleans directory has already been updated to the >> new policy and the class directory has not. The full solution is of >> course atomic swapover, which as I mentioned above I hope to submit a >> series for soon, but I wonder if recreating the directories on the >> old policy would be a better interim state?  That probably depends on >> what sorts of errors are possible.  If we've failed because of >> something about the new policy, recreating the old directories should >> get us back to a good state.  If we can't create new directories at >> all for whatever reason, trying to recreate might leave us worse off >> than before we started. > > I deliberately avoided any changes to the error handling during > re-creation of the booleans and class directories because I viewed > that as logically separate from my change and likely to conflict with > your changes.  So I expect to revisit that issue after both my patches > and yours land. I think the only scenario where > sel_make_bools/classes() can fail is an out-of-memory condition and if > we are out of memory then we are unlikely to be able to re-create the > old directories/files again.  Hence, I don't think there is anything > useful we can do without the atomic swapover. At most, we can delete > everything under booleans and class on any failure while re-creating > so that we aren't left with the partial set of booleans/classes. > > The other possibility I considered is explicitly checking whether > there are any changes to booleans or classes between the old and new > policies and if not, skipping that part of the selinuxfs update.  That > however would require a new security server function to iterate over > all of the booleans and classes in two selinux_policy structures and > compare them for equality.  Didn't seem worth it if the atomic > swapover support was coming anyway. > Sounds good. -Daniel