From: Oleg Nesterov <oleg@redhat.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
David Howells <dhowells@redhat.com>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Rik van Riel <riel@redhat.com>,
Vladimir Davydov <vdavydov@parallels.com>,
Ricky Zhou <rickyz@chromium.org>, Julien Tinnes <jln@google.com>
Subject: Re: [PATCH] user_ns: use correct check for single-threadedness
Date: Wed, 5 Aug 2015 19:23:56 +0200 [thread overview]
Message-ID: <20150805172356.GA20490@redhat.com> (raw)
In-Reply-To: <20150728221111.GA23391@node.dhcp.inet.fi>
On 07/29, Kirill A. Shutemov wrote:
>
> On Tue, Jul 28, 2015 at 02:35:04PM -0700, Andrew Morton wrote:
> > On Tue, 28 Jul 2015 10:15:00 -0700 Kees Cook <keescook@chromium.org> wrote:
> >
> > > From: Ricky Zhou <rickyz@chromium.org>
> > >
> > > Checking mm_users > 1 does not mean a process is multithreaded. For
> > > example, reading /proc/PID/maps temporarily increments mm_users, allowing
> > > other processes to (accidentally) interfere with unshare() calls.
> > >
> > > This fixes observed failures of unshare(CLONE_NEWUSER) incorrectly
> > > returning EINVAL if another processes happened to be simultaneously
> > > reading the maps file.
> >
> > Yikes. current_is_single_threaded() is expensive. Are we sure this
> > isn't going to kill someone's workload?
>
> It's expensive only if mm_users > 1. We will go to for_each_process() only
> if somebody outside of the process grabs mm_users references (like reading
> /proc/PID/maps).
Yes,
> Or if it called it from multithreaded application.
Not really, please note the "negative fast-path" check:
if (atomic_read(&task->signal->live) != 1)
return false;
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Same here, I think the patch is fine.
I don't think that sys_setns() is performance critical, and Eric seems
to agree with this change too.
Oleg.
next prev parent reply other threads:[~2015-08-05 17:26 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-28 17:15 [PATCH] user_ns: use correct check for single-threadedness Kees Cook
2015-07-28 18:02 ` Rik van Riel
2015-07-28 18:17 ` Eric W. Biederman
2015-07-28 20:55 ` Ricky Zhou
2015-07-28 21:01 ` Kees Cook
2015-08-05 18:13 ` Eric W. Biederman
2015-08-05 19:40 ` Kees Cook
2015-07-28 21:35 ` Andrew Morton
2015-07-28 21:50 ` Kees Cook
2015-07-28 22:11 ` Kirill A. Shutemov
2015-08-05 11:38 ` Ingo Molnar
2015-08-05 11:53 ` Kirill A. Shutemov
2015-08-05 13:13 ` Ricky Zhou
2015-08-05 17:23 ` Oleg Nesterov [this message]
2015-08-05 18:00 ` Eric W. Biederman
2015-08-05 18:52 ` Eric W. Biederman
2015-08-06 13:06 ` Oleg Nesterov
2015-08-06 13:44 ` Oleg Nesterov
2015-08-12 1:17 ` Eric W. Biederman
2015-08-12 14:40 ` Oleg Nesterov
2015-08-12 15:11 ` Eric W. Biederman
2015-08-12 1:22 ` [PATCH 0/2] userns: Creation logic fixes Eric W. Biederman
2015-08-12 1:24 ` [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm Eric W. Biederman
2015-08-12 17:48 ` Oleg Nesterov
2015-08-12 18:39 ` Eric W. Biederman
2015-08-13 12:55 ` Oleg Nesterov
2015-08-13 15:38 ` Eric W. Biederman
2015-08-13 16:17 ` Oleg Nesterov
2015-08-13 16:27 ` Eric W. Biederman
2015-08-13 16:50 ` Oleg Nesterov
2015-08-14 17:59 ` Oleg Nesterov
2015-08-12 19:59 ` [PATCH v2] " Eric W. Biederman
2015-08-13 12:57 ` Oleg Nesterov
2015-08-13 16:01 ` Eric W. Biederman
2015-08-13 16:30 ` Oleg Nesterov
2015-08-13 16:39 ` Eric W. Biederman
2015-08-12 1:25 ` [PATCH 2/2] userns,pidns: Force thread group sharing, not signal handler sharing Eric W. Biederman
2015-08-12 17:24 ` Oleg Nesterov
2015-08-12 6:29 ` [PATCH 0/2] userns: Creation logic fixes Kees Cook
2015-08-06 14:35 ` [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov
2015-08-06 21:16 ` Eric W. Biederman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150805172356.GA20490@redhat.com \
--to=oleg@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=dhowells@redhat.com \
--cc=ebiederm@xmission.com \
--cc=jln@google.com \
--cc=keescook@chromium.org \
--cc=kirill.shutemov@linux.intel.com \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=rickyz@chromium.org \
--cc=riel@redhat.com \
--cc=vdavydov@parallels.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).