Date:	Thu, 2 Feb 2012 09:32:32 -0600
From:	"Serge E. Hallyn" <serge.hallyn@...onical.com>
To:	Will Drewry <wad@...omium.org>
Cc:	linux-kernel@...r.kernel.org, keescook@...omium.org,
	john.johansen@...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,
	luto@....edu, 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 v6 2/3] seccomp_filters: system call filtering using BPF

Quoting Will Drewry (wad@...omium.org):
> [This patch depends on luto@....edu's no_new_privs patch:
>  https://lkml.org/lkml/2012/1/12/446
> ]
> 
> This patch adds support for seccomp mode 2.  This mode enables dynamic
> enforcement of system call filtering policy in the kernel as specified
> by a userland task.  The policy is expressed in terms of a Berkeley
> Packet Filter program, as is used for userland-exposed socket filtering.
> Instead of network data, the BPF program is evaluated over struct
> seccomp_filter_data at the time of the system call.
> 
> A filter program may be installed by a userland task by calling
>   prctl(PR_ATTACH_SECCOMP_FILTER, &fprog);
> where fprog is of type struct sock_fprog.
> 
> If the first filter program allows subsequent prctl(2) calls, then
> additional filter programs may be attached.  All attached programs
> must be evaluated before a system call will be allowed to proceed.
> 
> To avoid CONFIG_COMPAT related landmines, once a filter program is
> installed using specific is_compat_task() value, it is not allowed to
> make system calls using the alternate entry point.
> 
> Filter programs will be inherited across fork/clone and execve, however
> the installation of filters must be preceded by setting 'no_new_privs'
> to ensure that unprivileged tasks cannot attach filters that affect
> privileged tasks (e.g., setuid binary).  Tasks with CAP_SYS_ADMIN
> in their namespace may install inheritable filters without setting
> the no_new_privs bit.
> 
> There are a number of benefits to this approach. A few of which are
> as follows:
> - BPF has been exposed to userland for a long time.
> - Userland already knows its ABI: system call numbers and desired
>   arguments
> - No time-of-check-time-of-use vulnerable data accesses are possible.
> - system call arguments are loaded on demand only to minimize copying
>   required for system call number-only policy decisions.
> 
> This patch includes its own BPF evaluator, but relies on the
> net/core/filter.c BPF checking code.  It is possible to share
> evaluators, but the performance sensitive nature of the network
> filtering path makes it an iterative optimization which (I think :) can
> be tackled separately via separate patchsets. (And at some point sharing
> BPF JIT code!)
> 
>  v6: - fix memory leak on attach compat check failure
>      - require no_new_privs || CAP_SYS_ADMIN prior to filter
>        installation. (luto@....edu)
>      - s/seccomp_struct_/seccomp_/ for macros/functions
>        (amwang@...hat.com)
>      - cleaned up Kconfig (amwang@...hat.com)
>      - on block, note if the call was compat (so the # means something)
>  v5: - uses syscall_get_arguments
>        (indan@....nu,oleg@...hat.com, mcgrathr@...omium.org)
>      - uses union-based arg storage with hi/lo struct to
>        handle endianness.  Compromises between the two alternate
>        proposals to minimize extra arg shuffling and account for
>        endianness assuming userspace uses offsetof().
>        (mcgrathr@...omium.org, indan@....nu)
>      - update Kconfig description
>      - add include/seccomp_filter.h and add its installation
>      - (naive) on-demand syscall argument loading
>      - drop seccomp_t (eparis@...hat.com)
>  v4: - adjusted prctl to make room for PR_[SG]ET_NO_NEW_PRIVS
>      - now uses current->no_new_privs
>          (luto@....edu,torvalds@...ux-foundation.com)
>      - assign names to seccomp modes (rdunlap@...otime.net)
>      - fix style issues (rdunlap@...otime.net)
>      - reworded Kconfig entry (rdunlap@...otime.net)
>  v3: - macros to inline (oleg@...hat.com)
>      - init_task behavior fixed (oleg@...hat.com)
>      - drop creator entry and extra NULL check (oleg@...hat.com)
>      - alloc returns -EINVAL on bad sizing (serge.hallyn@...onical.com)
>      - adds tentative use of "always_unprivileged" as per
>        torvalds@...ux-foundation.org and luto@....edu
>  v2: - (patch 2 only)
> 
> Signed-off-by: Will Drewry <wad@...omium.org>

Hi Will,

as far as I can tell based on changelog I suspect you could have
kept my Acked-by (from v3?).  However, I'll wait until your next
submission (as I see there were a few change requests), and do a
final complete new review of that.

Thanks for continuing to push on this.

-serge
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