linux-kernel - Re: [PATCH] inotify: Convert to using per-namespace limits

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Date:   Mon, 10 Oct 2016 09:44:19 +0300
From:   Nikolay Borisov <kernel@...p.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     john@...nmccutchan.com, eparis@...isplace.org,
        viro@...iv.linux.org.uk, jack@...e.cz, serge@...lyn.com,
        avagin@...nvz.org, linux-kernel@...r.kernel.org,
        containers@...ts.linux-foundation.org
Subject: Re: [PATCH] inotify: Convert to using per-namespace limits



On 10/07/2016 09:14 PM, Eric W. Biederman wrote:
> Nikolay Borisov <kernel@...p.com> writes:
> 
>> This patchset converts inotify to using the newly introduced
>> per-userns sysctl infrastructure.
>>
>> Currently the inotify instances/watches are being accounted in the
>> user_struct structure. This means that in setups where multiple
>> users in unprivileged containers map to the same underlying
>> real user (i.e. pointing to the same user_struct) the inotify limits
>> are going to be shared as well, allowing one user(or application) to exhaust
>> all others limits.
>>
>> Fix this by switching the inotify sysctls to using the
>> per-namespace/per-user limits. This will allow the server admin to
>> set sensible global limits, which can further be tuned inside every
>> individual user namespace.
>>
>> Signed-off-by: Nikolay Borisov <kernel@...p.com>
>> ---
>> Hello Eric, 
>>
>> I saw you've finally sent your pull request for 4.9 and it 
>> includes your implementatino of the ucount infrastructure. So 
>> here is my respin of the inotify patches using that.
> 
> Thanks.  I will take a good hard look at this after -rc1 when things are
> stable enough that I can start a new development branch.
> 
> I am a little concerned that the old sysctls have gone away.  If no one
> cares it is fine, but if someone depends on them existing that may count
> as an unnecessary userspace regression.  But otherwise skimming through
> this code it looks good.

So this indeed this is real issue and I meant to write something about
it. Anyway, in order to preserve those sysctl what can be done is to
hook them up with a custom sysctl handler taking the ns from the proc
mount and the euid of current? I think this is a good approach, but
let's wait and see if anyone will have objections to completely
eliminating those sysctls.


> 
[SNIP]