From: Djalal Harouni <tixxdz@opendz.org>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
"Serge E. Hallyn" <serge.hallyn@ubuntu.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>,
tixxdz@gmail.com
Subject: Re: [PATCH 04/12] seq_file: Make seq_file able to access the file's opener cred
Date: Sat, 28 Sep 2013 15:57:26 +0100 [thread overview]
Message-ID: <20130928145725.GB2199@dztty> (raw)
In-Reply-To: <20130926030254.GF13318@ZenIV.linux.org.uk>
On Thu, Sep 26, 2013 at 04:02:54AM +0100, Al Viro wrote:
> On Wed, Sep 25, 2013 at 05:22:51PM -0700, Linus Torvalds wrote:
> > On Wed, Sep 25, 2013 at 1:14 PM, Djalal Harouni <tixxdz@opendz.org> wrote:
> > >
> > > Therefor add the f_cred field to the seq_file struct and a helper
> > > seq_f_cred() to return it.
> >
> > I hate how you've split up this patch from the next one that actually
> > _initializes_ the new field.
> >
> > The two patches should have been one.
> >
> > I think the patch should also remove the 'user_ns' member, since it's
> > now available as f_cred->user_ns.
> >
> > I also suspect that it would be better to just make the the new
> > seq_file member point to the 'struct file' instead. Sure, it's an
> > extra level of indirection, but the lifetime of f_cred is not as clear
> > otherwise. You don't increment the reference count, which is correct
> > *only* because 'seq_file' has the same lifetime as 'struct file', and
> > thus the reference count from struct file for the f_cred is
> > sufficient.
>
> That's better than f_cred (or user_ns, for that matter), but... I'm
> afraid that it'll get abused very soon. And I don't understand the
> argument about the lifetime rules - what makes struct file ones
> different from struct cred ones in that respect? Except that in this
> case it's really obvious that we can't grab a reference, that is...
For that reference count lifetime rule. Sorry I was trying to compare it
with other implemented solutions. /proc/pid/environ will increment the
mm->mm_count inside __mem_open(), thus mm_struct will stay in until
mem_release(). That's it.
In the proposed solution and as noted by Linus, the reference count
from 'struct file' is sufficient for f_cred.
Last, I'm happy with /proc/pid/environ as it is, will not touch it
unless there is a request for it, but this proposed file->f_cred
solution is better:
* Not *all* these /proc/<pid>/* files are interested in acquiring a
reference to the task's mm and increment its counters.
* It can be adapted to all the /proc/<pid>/* files, we already have the
file->f_cred
* It allow to pass file descriptors if original opener had enough
permission. It's explained in [Patch 0/12]
* It allow referencing the correct mm of the currently running
target task at read(),write()...
Where other solutions will just block/restrict this behaviour.
Thanks
--
Djalal Harouni
http://opendz.org
next prev parent reply other threads:[~2013-09-28 14:57 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-25 20:14 [PATCH 0/12] procfs: protect /proc/<pid>/* files with file->f_cred Djalal Harouni
2013-09-25 20:14 ` [PATCH 01/12] procfs: add proc_same_open_cred() to check if the cred have changed Djalal Harouni
2013-09-25 20:14 ` [PATCH 02/12] procfs: add proc_allow_access() to check if file's opener may access task Djalal Harouni
2013-09-25 20:14 ` [PATCH 03/12] procfs: Document the proposed solution to protect procfs entries Djalal Harouni
2013-09-25 20:14 ` [PATCH 04/12] seq_file: Make seq_file able to access the file's opener cred Djalal Harouni
2013-09-26 0:22 ` Linus Torvalds
2013-09-26 3:02 ` Al Viro
2013-09-27 8:37 ` Djalal Harouni
2013-09-28 14:57 ` Djalal Harouni [this message]
2013-09-27 8:34 ` Djalal Harouni
2013-09-26 2:42 ` Al Viro
2013-09-25 20:14 ` [PATCH 05/12] seq_file: set the seq_file->f_cred during seq_open() Djalal Harouni
2013-09-25 20:14 ` [PATCH 06/12] procfs: make /proc/*/stack 0400 Djalal Harouni
2013-09-26 20:43 ` Kees Cook
2013-09-28 14:35 ` Djalal Harouni
2013-10-02 19:52 ` Kees Cook
2013-09-29 10:37 ` Djalal Harouni
2013-10-02 19:49 ` Kees Cook
2013-09-25 20:14 ` [PATCH 07/12] procfs: add permission checks on the file's opener of /proc/*/stack Djalal Harouni
2013-09-25 20:14 ` [PATCH 08/12] procfs: add permission checks on the file's opener of /proc/*/personality Djalal Harouni
2013-09-25 20:14 ` [PATCH 09/12] procfs: add permission checks on the file's opener of /proc/*/stat Djalal Harouni
2013-09-25 20:14 ` [PATCH 10/12] procfs: move PROC_BLOCK_SIZE declaration up to make it visible Djalal Harouni
2013-09-25 20:14 ` [PATCH 11/12] procfs: improve permission checks on /proc/*/syscall Djalal Harouni
2013-09-25 20:14 ` [PATCH 12/12] user_ns: seq_file: use the user_ns that is embedded in the f_cred struct Djalal Harouni
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