linux-kernel - Re: [PATCH v10 06/11] seccomp: add SECCOMP_RET

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Message-ID: <CABqD9hburo_4Yz+figsSOExun3ckft3UrZpOZTw+aywmCKy-rg@mail.gmail.com>
Date:	Tue, 21 Feb 2012 16:48:05 -0600
From:	Will Drewry <wad@...omium.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
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	mcgrathr@...omium.org, tglx@...utronix.de, luto@....edu,
	eparis@...hat.com, serge.hallyn@...onical.com, djm@...drot.org,
	scarybeasts@...il.com, indan@....nu, pmoore@...hat.com,
	akpm@...ux-foundation.org, corbet@....net, eric.dumazet@...il.com,
	markus@...omium.org
Subject: Re: [PATCH v10 06/11] seccomp: add SECCOMP_RET_ERRNO

On Tue, Feb 21, 2012 at 4:41 PM, Kees Cook <keescook@...omium.org> wrote:
> On Tue, Feb 21, 2012 at 11:30:30AM -0600, Will Drewry wrote:
>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>> index 0043b7e..23f1844 100644
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -136,22 +136,18 @@ static void *bpf_load(const void *nr, int off, unsigned int size, void *buf)
>>  static u32 seccomp_run_filters(int syscall)
>>  {
>>       struct seccomp_filter *f;
>> -     u32 ret = SECCOMP_RET_KILL;
>>       static const struct bpf_load_fn fns = {
>>               bpf_load,
>>               sizeof(struct seccomp_data),
>>       };
>> +     u32 ret = SECCOMP_RET_ALLOW;
>>       const void *sc_ptr = (const void *)(uintptr_t)syscall;
>> -
>>       /*
>>        * All filters are evaluated in order of youngest to oldest. The lowest
>>        * BPF return value always takes priority.
>>        */
>> -     for (f = current->seccomp.filter; f; f = f->prev) {
>> -             ret = bpf_run_filter(sc_ptr, f->insns, &fns);
>> -             if (ret != SECCOMP_RET_ALLOW)
>> -                     break;
>> -     }
>> +     for (f = current->seccomp.filter; f; f = f->prev)
>> +             ret = min_t(u32, ret, bpf_run_filter(sc_ptr, f->insns, &fns));
>>       return ret;
>>  }
>
> I'd like to see this fail closed in the (theoretically impossible, but
> why risk it) case of there being no filters at all. Could do something
> like this:
>
>        u32 ret = current->seccomp.filter ? SECCOMP_RET_ALLOW : SECCOMP_RET_KILL;
>
> Or, just this, to catch the misbehavior:
>
>        if (unlikely(current->seccomp.filter == NULL))
>                return SECCOMP_RET_KILL;

I think the last one makes the most sense to me.  I'll add it and rev the patch.

thanks!
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