linux-kernel - Re: [PATCH v5 2/3] seccomp_filters: system call filtering using BPF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CABqD9hYbtR3ROU9RDG6=PxFz9mXZMJDNynU40SiOCEw+pct9dA@mail.gmail.com>
Date:	Sat, 28 Jan 2012 11:50:57 -0800
From:	Will Drewry <wad@...omium.org>
To:	Andrew Lutomirski <luto@....edu>
Cc:	linux-kernel@...r.kernel.org, keescook@...omium.org,
	john.johansen@...onical.com, serge.hallyn@...onical.com,
	coreyb@...ux.vnet.ibm.com, pmoore@...hat.com, eparis@...hat.com,
	djm@...drot.org, torvalds@...ux-foundation.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	oleg@...hat.com, ak@...ux.intel.com, eric.dumazet@...il.com,
	gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com, corbet@....net,
	alan@...rguk.ukuu.org.uk, indan@....nu, mcgrathr@...omium.org
Subject: Re: [PATCH v5 2/3] seccomp_filters: system call filtering using BPF

On Sat, Jan 28, 2012 at 8:28 AM, Andrew Lutomirski <luto@....edu> wrote:
> On Fri, Jan 27, 2012 at 3:24 PM, Will Drewry <wad@...omium.org> wrote:
>> Filter programs will be inherited across fork/clone and execve.
>> However, if the task attaching the filter is unprivileged
>> (!CAP_SYS_ADMIN) the no_new_privs bit will be set on the task.  This
>> ensures that unprivileged tasks cannot attach filters that affect
>> privileged tasks (e.g., setuid binary).
>
> This makes me nervous -- I don't think that the behavior of any new
> API should be different depending on privilege level -- adding a
> privilege should just make things work that would otherwise fail.  You
> might end up with bugs where a program is completely safe if run
> without CAP_SYS_ADMIN but, if run with CAP_SYS_ADMIN, bad things
> happen.  (The behavior of setuid(geteuid()) is an example of this
> problem.)
>
> One way to fix it is to make setting a filter program fail unless
> capable(CAP_SYS_ADMIN ) || no_new_privs.

Good call.  I'll upgrade the interaction with no_new_privs to be
explicit in the next revision.  It is certainly more transparent and
removes the risk of unintended consequences.

thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/