From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
Tejun Heo <tj@kernel.org>, Andrew Vagin <avagin@openvz.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
Pavel Emelyanov <xemul@parallels.com>,
Vasiliy Kulikov <segoon@openwall.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [RFC 2/2] prctl: PR_SET_MM -- Introduce PR_SET_MM_MAP operation
Date: Wed, 9 Jul 2014 02:13:36 +0400 [thread overview]
Message-ID: <20140708221336.GL17860@moon.sw.swsoft.com> (raw)
In-Reply-To: <20140708143830.ea078ef01e1d7d31276edbcd@linux-foundation.org>
On Tue, Jul 08, 2014 at 02:38:30PM -0700, Andrew Morton wrote:
> On Tue, 8 Jul 2014 23:08:49 +0400 Cyrill Gorcunov <gorcunov@gmail.com> wrote:
>
> > Ping. Guys, any commens please?
>
> Well, allowing a process to modify pretty deep internals like this is
> always scary from a security point of view, and now we're removing
> CAP_SYS_RESOURCE protections. Yikes. Convince me we aren't handing
> out root here.
>
> The changelog doesn't make it clear (to me) why this is actually being
> done. criu runs unprivileged? What's the requirement here?
It comes from user-ns, we are almost ready to support c/r for user
namespaces and faced a problem -- when we create new user-namespace
we loose CAP_SYS_RESOURCE bit and criu fails to proceed. Andrew
Vagin was implementing user-ns in criu and as far as I remember
there were a talk with Eric which (again if my memory doesn't
betray me) end up in -- guys, simply do proper check for values
you read from user space instead of relying on CAP_SYS_RESOURCE.
Erik, am I right?
Probably I should walk over _every_ member we're modifying
explaning where exactly is used in kernel.
Still the good news about all this members we modify -- they are used
for statistics mostly except brk/stack related members but they
are checked very carefully to not exceed the limits (if the
limits are set).
> struct prctl_mm_map could do with a nice comment explaining its role in
> the world.
ok, i'll update
> I'm not seeing a coherent description of the proposed userspace
> interface. We'll eventually want to update the prctl manpage for this,
> so how about laying out all the needed details now, at patch review
> time so we can see what is proposed.
Sure, I'll write more descriptive comment since original "It takes
a pointer of prctl_mm_map structure which carries all members to be
updated" is too short.
>
> Why isn't the newly-added code under #ifdef CONFIG_CHECKPOINT_RESTORE?
Initially all prctl set-mm opcodes were CONFIG_CHECKPOINT_RESTORE
guarded but then assumed that such modification might be
needed not only for criu but other tools as well and this #ifdef
were dropped off. Now new PR_SET_MM_MAP is a part of old
interface so I'm not sure if it should be CONFIGed. That
said it is not a problem to wrap it but looks unreasonable
in this particular case.
next prev parent reply other threads:[~2014-07-08 22:13 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-03 14:33 [RFC 0/2] prctl: set-mm -- Rework interface Cyrill Gorcunov
2014-07-03 14:33 ` [RFC 1/2] prctl: PR_SET_MM -- Factor out mmap_sem when update mm::exe_file Cyrill Gorcunov
2014-07-03 14:33 ` [RFC 2/2] prctl: PR_SET_MM -- Introduce PR_SET_MM_MAP operation Cyrill Gorcunov
2014-07-03 20:34 ` Cyrill Gorcunov
2014-07-04 7:52 ` Andrew Vagin
2014-07-04 8:11 ` Cyrill Gorcunov
2014-07-08 19:08 ` Cyrill Gorcunov
2014-07-08 21:38 ` Andrew Morton
2014-07-08 22:13 ` Cyrill Gorcunov [this message]
2014-07-09 14:13 ` Cyrill Gorcunov
2014-07-09 14:53 ` Kees Cook
2014-07-09 15:06 ` Cyrill Gorcunov
2014-07-11 17:36 ` Cyrill Gorcunov
2014-07-22 20:07 ` Kees Cook
2014-07-22 20:36 ` Cyrill Gorcunov
2014-07-24 13:48 ` Andrew Vagin
2014-07-24 16:42 ` Cyrill Gorcunov
2014-07-24 18:44 ` Kees Cook
2014-07-24 18:50 ` Cyrill Gorcunov
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