linux-kernel - Re: [PATCH 0/5] userns: bump idmap limits, fixes & tweaks

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Message-ID: <87tvyemeqe.fsf@xmission.com>
Date:   Wed, 01 Nov 2017 06:15:53 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Christian Brauner <christian.brauner@...onical.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Serge Hallyn <serge@...lyn.com>,
        Tycho Andersen <tycho@...ho.ws>,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH 0/5] userns: bump idmap limits, fixes & tweaks

Christian Brauner <christian.brauner@...onical.com> writes:

> On Tue, Oct 31, 2017 at 06:46:32PM -0500, Eric W. Biederman wrote:
>>
>> Christian I have looked through your code and I have found one real
>> issue and of things I want to twak
>
> Cool, thanks for taking a close look Eric.
>
>>
>> The real issue is reading nr_extents multiple times when reading a map.
>> That can introduce races that will allow walking past the end of the
>> array, if the first read is 0 but the second read is > 5.
>>
>> I have also found a couple of tweaks that look like they are worth
>> implementing.
>
> Yeah, I saw that you unified some of the functions. I was thinking about this
> but wanted to keep the cases distinct even with some amount of code duplication.
> But it seems very much worth it from a maintenance perspective. Thanks!

Yes.  If we have a performance regression I am willing to remove the
unification of map_id_range_down and map_id_down.  But I can't imagine
that will result in a measurable performance difference.  If it does
make a measurable perforamnce difference we almost certainly need to split
the bsearch case as well.

>> As all of these are very small and very straight forward I have
>> tested these and applied them all to my for-next branch
>
> Thanks for the fixes Eric. Really appreciated. If you're too swamped for stuff
> like that I'm obviously happy to do such trivial fixes myself. :)

If you would test this some more in your setup I would appreciate it,
just in case I missed something.

Given where we are in the development cycle and the correctness concerns
I just applied these as without the fix for reading extents exactly once
the code is dangerously wrong.

Eric

> Christian
>
>>
>>
>> Eric W. Biederman (5):
>>       userns: Don't special case a count of 0
>>       userns: Simplify the user and group mapping functions
>>       userns: Don't read extents twice in m_start
>>       userns: Make map_id_down a wrapper for map_id_range_down
>>       userns: Simplify insert_extent
>>
>>  kernel/user_namespace.c | 159 ++++++++++++++++--------------------------------
>>  1 file changed, 51 insertions(+), 108 deletions(-)
>>
>>
>>
>>