From: "Luis R. Rodriguez" <mcgrof@kernel•org>
To: Kees Cook <keescook@chromium•org>
Cc: "Luis R. Rodriguez" <mcgrof@kernel•org>,
Djalal Harouni <tixxdz@gmail•com>,
Andy Lutomirski <luto@kernel•org>,
Andrew Morton <akpm@linux-foundation•org>,
James Morris <james.l.morris@oracle•com>,
Ben Hutchings <ben.hutchings@codethink•co.uk>,
Solar Designer <solar@openwall•com>,
Serge Hallyn <serge@hallyn•com>, Jessica Yu <jeyu@kernel•org>,
Rusty Russell <rusty@rustcorp•com.au>,
LKML <linux-kernel@vger•kernel.org>,
linux-security-module <linux-security-module@vger•kernel.org>,
kernel-hardening@lists•openwall.com,
Jonathan Corbet <corbet@lwn•net>, Ingo Molnar <mingo@kernel•org>,
"David S. Miller" <davem@davemloft•net>,
Network Development <netdev@vger•kernel.org>,
Peter Zijlstra <peterz@infradead•org>,
Linus Torvalds <torvalds@linux-foundation•org>
Subject: Re: [PATCH v5 next 1/5] modules:capabilities: add request_module_cap()
Date: Tue, 28 Nov 2017 23:48:49 +0100 [thread overview]
Message-ID: <20171128224849.GT729@wotan.suse.de> (raw)
In-Reply-To: <CAGXu5jKqMeBUB4iArqw9_iyKqm3NjpCrU_byy90kZrAHDb0c9w@mail.gmail.com>
On Tue, Nov 28, 2017 at 02:18:18PM -0800, Kees Cook wrote:
> On Tue, Nov 28, 2017 at 2:12 PM, Luis R. Rodriguez <mcgrof@kernel•org> wrote:
> > On Tue, Nov 28, 2017 at 01:39:58PM -0800, Kees Cook wrote:
> >> On Tue, Nov 28, 2017 at 1:16 PM, Luis R. Rodriguez <mcgrof@kernel•org> wrote:
> >> > And *all* auto-loading uses aliases? What's the difference between auto-loading
> >> > and direct-loading?
> >>
> >> The difference is the process privileges. Unprivilged autoloading
> >> (e.g. int n_hdlc = N_HDLC; ioctl(fd,
> >> TIOCSETD, &n_hdlc)), triggers a privileged call to finit_module()
> >> under CAP_SYS_MODULE.
> >
> > Ah, so system call implicated request_module() calls.
>
> Yup. Unprivileged user does something that ultimately hits a
> request_module() in the kernel. Then the kernel calls out with the
> usermode helper (which has CAP_SYS_MODULE) and calls finit_module().
Thanks, using this terminology is much better to understand than auto-loading,
given it does make it clear an unprivileged call was one that initiated the
request_module() call, there are many uses of request_module() which *are*
privileged.
> > OK and since CAP_SYS_MODULE is much more restrictive one could argue, what's the
> > point here?
>
> The goal is to block an unprivileged user from being able to trigger a
> module load without blocking root from loading modules directly.
I see now. Do we have an audit of all system calls which implicate a
request_module() call? Networking is a good example for sure to start
off with but I was curious if we have a grasp of how wide spread this
could be.
I'll go review the patches again now with all this in mind.
Luis
next prev parent reply other threads:[~2017-11-28 22:48 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-27 17:18 [PATCH v5 next 0/5] Improve Module autoloading infrastructure Djalal Harouni
2017-11-27 17:18 ` [PATCH v5 next 1/5] modules:capabilities: add request_module_cap() Djalal Harouni
2017-11-27 18:48 ` Randy Dunlap
2017-11-27 21:35 ` Djalal Harouni
2017-11-28 19:14 ` Luis R. Rodriguez
2017-11-28 20:11 ` Kees Cook
2017-11-28 21:16 ` Luis R. Rodriguez
2017-11-28 21:33 ` Djalal Harouni
2017-11-28 22:18 ` Luis R. Rodriguez
2017-11-28 22:52 ` Djalal Harouni
2017-11-28 21:39 ` Kees Cook
2017-11-28 22:12 ` Luis R. Rodriguez
2017-11-28 22:18 ` Kees Cook
2017-11-28 22:48 ` Luis R. Rodriguez [this message]
2017-11-29 7:49 ` Michal Kubecek
2017-11-29 13:46 ` Alan Cox
2017-11-29 14:50 ` David Miller
2017-11-29 15:54 ` Theodore Ts'o
2017-11-29 15:58 ` David Miller
2017-11-29 16:29 ` Theodore Ts'o
2017-11-29 22:45 ` Linus Torvalds
2017-11-30 0:06 ` Kees Cook
2017-11-29 17:28 ` Serge E. Hallyn
2017-11-30 0:35 ` Theodore Ts'o
2017-11-30 17:17 ` Serge E. Hallyn
2017-11-28 20:18 ` Djalal Harouni
2017-11-27 17:18 ` [PATCH v5 next 2/5] modules:capabilities: add cap_kernel_module_request() permission check Djalal Harouni
2017-11-30 2:05 ` Luis R. Rodriguez
2017-11-27 17:18 ` [PATCH v5 next 3/5] modules:capabilities: automatic module loading restriction Djalal Harouni
2017-11-30 1:23 ` Luis R. Rodriguez
2017-11-30 12:22 ` Djalal Harouni
2017-11-27 17:18 ` [PATCH v5 next 4/5] modules:capabilities: add a per-task modules auto-load mode Djalal Harouni
2017-11-27 17:18 ` [PATCH v5 next 5/5] net: modules: use request_module_cap() to load 'netdev-%s' modules Djalal Harouni
2017-11-27 18:44 ` Linus Torvalds
2017-11-27 21:41 ` Djalal Harouni
2017-11-27 22:04 ` Linus Torvalds
2017-11-27 22:59 ` Kees Cook
2017-11-27 23:14 ` Linus Torvalds
2017-11-27 23:19 ` Kees Cook
2017-11-27 23:35 ` Linus Torvalds
2017-11-28 1:23 ` Kees Cook
2017-11-27 18:41 ` [PATCH v5 next 0/5] Improve Module autoloading infrastructure Linus Torvalds
2017-11-27 19:02 ` Linus Torvalds
2017-11-27 19:12 ` Linus Torvalds
2017-11-27 21:31 ` Djalal Harouni
2017-11-27 19:14 ` David Miller
2017-11-27 22:31 ` James Morris
2017-11-27 23:04 ` Kees Cook
2017-11-27 23:44 ` James Morris
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