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Message-ID: <20170217171136.GA23766@uranus>
Date: Fri, 17 Feb 2017 20:11:36 +0300
From: Cyrill Gorcunov <gorcunov@...il.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: Linux FS Devel <linux-fsdevel@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...uxfoundation.org>,
Andrew Vagin <avagin@...tuozzo.com>,
Pavel Emelyanov <xemul@...tuozzo.com>,
Michael Kerrisk <mtk.manpages@...il.com>,
Kirill Kolyshkin <kir@...nvz.org>,
Andrey Vagin <avagin@...nvz.org>
Subject: Re: [RFC 1/2] fs,eventpoll: Add ability to install target file by
its number
On Fri, Feb 17, 2017 at 08:52:59AM -0800, Andy Lutomirski wrote:
> >
> > To resolve this tie lets add EPOLL_CTL_DUP operation which simply takes
> > target file descriptor number and installs it into a caller's file table,
> > thus we can use kcmp() syscall and figure out which exactly file to be
> > added into eventpoll on restore procedure.
>
> This is a scary thing to let an unprivileged process do.
>
> I'm wondering if there might be a nicer way to address this using a
> better interface in /proc.
Well, I tend to agree. Need to add security checking if the target
file is accessable by a caller. As to better interface to procfs
nothing comes to mind immediately. Another potential problem is that
since it is never guaranteed that target file number listed in fdinfo
matching existing /proc/pid/fd/N, so that I think we will have to
use this dup functionality for every target file, which of course
not that fast. Probably need to think more if I manage to invent
some better and faster interface to find where exactly target file
belong in the whole process tree of a container.
Thanks for pointing about this security problem, Andy!
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