Re: [PATCH v2 3/4] seccomp: Create an action to log before allowing

[Tyler Hicks <tyhicks@canonical.com>]

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On 02/10/2017 06:08 PM, Kees Cook wrote:
> On Fri, Feb 10, 2017 at 4:01 PM, Tyler Hicks <tyhicks@canonical.com> wrote:
>> On 02/07/2017 06:33 PM, Kees Cook wrote:
>>> This adds to UAPI, so it'd be good to think for a moment about how
>>> this would work on older kernels: right now, if someone tried to use
>>> this RET_LOG on an old kernel, it'll get treated like RET_KILL. Is
>>> this sane?
>>
>> It is not sane for userspace code to blindly attempt to use a new
>> feature on an old kernel. One of the main motivations of the
>> actions_avail sysctl is to allow userspace to be smart about what the
>> current kernel supports.
> 
> Yeah, agreed. I mean, userspace could also build a little test
> program, toss in RET_LOG, run it and see if it get SIGSYS. But that's
> so much more pain that checking in /proc.
> 
>> I'll be adding logic (requested by Paul) to libseccomp that checks this
>> sysctl when SECOMP_RET_LOG is attempted to be used. Programs that don't
>> use libseccomp will have to do something similar.
> 
> Excellent, I had been meaning to ask if you'd chatted with Paul at
> all, since this is an API addition for libseccomp.

We talked through some of it after the initial PR that I submitted to
libseccomp:

  https://github.com/seccomp/libseccomp/pull/64

I'll be updating that as we get closer to a land-able set of kernel patches.

> Speaking of which, can you CC linux-api@ on the next version too?

Yes, good idea!

Tyler



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