Message-ID: <CAGXu5jJSNfQs3Y7FgYs1LE0XsBsrCzzh8nOvLOQL4HFXqpD5WA@mail.gmail.com>
Date:   Wed, 1 Mar 2017 15:04:34 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Paul Moore <paul@...l-moore.com>
Cc:     "Reshetova, Elena" <elena.reshetova@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-audit@...hat.com" <linux-audit@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "tj@...nel.org" <tj@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "lizefan@...wei.com" <lizefan@...wei.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        Eric Paris <eparis@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "luto@...nel.org" <luto@...nel.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>
Subject: Re: [PATCH 15/19] kernel: convert audit_tree.count from atomic_t to refcount_t

On Wed, Mar 1, 2017 at 11:35 AM, Paul Moore <paul@...l-moore.com> wrote:
> On Tue, Feb 28, 2017 at 7:16 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Tue, Feb 28, 2017 at 2:11 PM, Paul Moore <paul@...l-moore.com> wrote:
>>> I just realized that include/linux/refcount.h didn't make it into
>>> v4.10 which means there is going to be delay until I merge them into
>>> the audit tree (I don't base the tree on -rc releases except under
>>> extreme circumstances).  I've got the patches queued up in a private
>>> holding branch (I added #includes BTW) so I won't forget, but as a
>>> FYI, they likely won't make it in until v4.12.
>>
>> I'm not asking for you to change this, but I am curious: doesn't that
>> force you to always be a release behind? I've tended to base trees on
>> -rc2 (and then the final release while the next merge window is open).
>> But that may be because I tend to have such wide dependencies...
>
> In general, yes ... and if you are just looking for the short answer
> I'd leave it at that.  I do leave door open for exceptions under
> unusual circumstances, but I don't believe the refcount_t conversion
> is one of those cases.

Right, totally agreed: doing refcount_t conversions is going to be a
long tail process, which is fine.

> The longer answer lies in a balancing act between what I understand
> Linus' and/or James desires (different upstream maintainers, different
> approaches, but for my own sanity I like to stick to a single
> "process" across my trees), the linux-next effort, branch stability
> (aka limited or predictable rebases), and my own testing requirements.
> First off, the current policy I follow for the SELinux and audit trees
> can be found here:
>
> * http://www.paul-moore.com/blog/d/2016/03/kernel-repo-process.html
>
> ... it's relatively simple and has proven to work reasonably well over
> the past year or so.  On occasion, the subsystem changes in a given
> release are significant enough that I skip a rebase (step #2 in the
> process) but that has only happened once (twice?) with the audit tree
> and didn't prove to be a real problem; this is less of an issue with
> the SELinux tree as James often rebases the linux-security tree to the
> current -rc1 or -rc2 tree.
>
> As for the balancing act ... My understanding is that Linus doesn't
> like to see pull requests from trees based on -rcX tags, he would much
> prefer to see trees based on a proper release, e.g. v4.10; on the plus
> side, Linus is willing to put up with some merge fuzzing so long as it
> is understandable and/or well explained.

Ah, hrm, yeah, I'd heard Linus mention that in the past, but when I
was talking with sfr about what's best for -next tree targets, he
mentioned -rc2 since it tends (in my understanding/memory of what he
told me) to be the least "noisy" position. Interesting!

> James wants pull requests
> that apply with zero merge conflicts to his linux-security/next tree;
> on the plus side, the linux-security/next tree tends to be based on
> the current -rc1/2 so a broad set of dependencies isn't too bad (which
> is important for SELinux).  The linux-next people want to see a commit
> ID follow a steady progression of multiple weeks in the subsystem
> -next branch and then a trickle up through various trees until it hits
> Linus' tree.  The branch stability requirements are pretty obvious,
> and with the exception of the -next branches during/immediately-after
> the merge window, I don't really rebase branches unless there is a
> Very Good Reason.  Finally, my own testing requirements are such that
> I want to test the current SELinux and audit -next/-stable branches
> against the latest bits in Linus' tree (e.g. -rcX releases) on a
> weekly basis so keeping those branches as current as possible is
> important; I talked a bit more about my testing at Flock 2016,
> slides/video at the link below:
>
> * http://www.paul-moore.com/blog/d/2016/08/flock-kernel-testing.html
> * https://copr.fedorainfracloud.org/coprs/pcmoore/kernel-secnext
>
> There ya go, probably more than you wanted to know, but that's why
> things are the way they are with the SELinux and audit trees.  I
> remain open to new ideas about how to manage the trees, but the
> current arrangement seems to work reasonably well at the moment.

Actually, no, this was great. Thanks! It's why I asked. :) Whenever I
see a maintainer with a different approach I try to figure out what
I'm missing, etc. :)

-Kees

-- 
Kees Cook
Pixel Security

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