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

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Date:   Mon, 10 Oct 2016 18:40:46 +0200
From:   Jan Kara <jack@...e.cz>
To:     Nikolay Borisov <kernel@...p.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        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 Mon 10-10-16 09:44:19, Nikolay Borisov wrote:
> 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.

Well, I believe just discarding those sysctls is not an option - I'm pretty
sure there are scripts out there which tune these sysctls and those would
stop working. IMO not acceptable regression.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR