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Date: Sat, 29 Oct 2016 14:04:37 -0700
From: Josh Triplett <josh@joshtriplett.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: David Herrmann <dh.herrmann@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Steven Rostedt <rostedt@goodmis.org>, Arnd Bergmann <arnd@arndb.de>,
        Tom Gundersen <teg@jklm.no>, Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC v1 00/14] Bus1 Kernel Message Bus
Message-ID: <20161029210437.la5opn65xxsdlrvb@x>
References: <20161026191810.12275-1-dh.herrmann@gmail.com>
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On Thu, Oct 27, 2016 at 03:45:24AM +0300, Kirill A. Shutemov wrote:
> On Wed, Oct 26, 2016 at 10:34:30PM +0200, David Herrmann wrote:
> > Long story short: We have uid<->uid quotas so far, which prevent DoS
> > attacks, unless you get access to a ridiculous amount of local UIDs.
> > Details on which resources are accounted can be found in the wiki [1].
> 
> Does only root user_ns uid count as separate or per-ns too?
> 
> In first case we will have vitually unbounded access to UIDs.
> 
> The second case can cap number of user namespaces a user can create while
> using bus1 inside.

That seems easy enough to solve.  Make the uid<->uid quota use uids in
the namespace of the side whose resources the operation uses.  That way,
if both sender and recipient live in a user namespace then you get quota
per user in the namespace, but you can't use a user namespace to cheat
and manufacture more users to get more quota when talking to something
*outside* that namespace.

- Josh Triplett