linux-kernel - Re: v5 of seccomp filter c/r patches

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Date:	Fri, 2 Oct 2015 16:00:45 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Tycho Andersen <tycho.andersen@...onical.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: v5 of seccomp filter c/r patches

On Fri, Oct 2, 2015 at 3:57 PM, Daniel Borkmann <daniel@...earbox.net> wrote:
> On 10/03/2015 12:44 AM, Tycho Andersen wrote:
>>
>> On Fri, Oct 02, 2015 at 02:10:24PM -0700, Kees Cook wrote:
>
> ...
>>
>> Ok, how about,
>>
>> struct sock_filter insns[BPF_MAXINSNS];
>> insn_cnt = ptrace(PTRACE_SECCOMP_GET_FILTER, pid, insns, i);
>
>
> Would also be good that when the storage buffer (insns) is NULL,
> it just returns you the number of sock_filter insns (or 0 when
> nothing attached).
>
> That would be consistent with classic socket filters (see
> sk_get_filter()), and user space could allocate a specific
> size instead of always passing in max insns.

Yes please. :)

>> when asking for the ith filter? It returns either the number of
>> instructions, -EINVAL if something was wrong (i, pid,
>> CONFIG_CHECKPOINT_RESTORE isn't enabled). While it would always
>> succeed now, if/when the underlying filter was not created from a bpf
>> classic filter, we can return -EMEDIUMTYPE? (Suggestions welcome, I
>> picked this mostly based on what sounds nice.)

We can bikeshed the non-classic case when we need it, but I think
EINVAL is "not under seccomp", and ENOENT is "no such index".

-Kees

-- 
Kees Cook
Chrome OS Security
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