Re: [PATCH 0/2] Begin auditing SECCOMP_RET_ERRNO return actions

[Paul Moore <paul@paul-moore.com>]

On Tue, Jan 3, 2017 at 8:31 AM, Tyler Hicks <tyhicks@canonical.com> wrote:
> On 01/02/2017 04:47 PM, Paul Moore wrote:
>> On Mon, Jan 2, 2017 at 11:53 AM, Tyler Hicks <tyhicks@canonical.com> wrote:
>>> This patch set creates the basis for auditing information specific to a given
>>> seccomp return action and then starts auditing SECCOMP_RET_ERRNO return
>>> actions. The audit messages for SECCOMP_RET_ERRNO return actions include the
>>> errno value that will be returned to userspace.
>>
>> I'm replying to this patchset posting because it his my inbox first,
>> but my comments here apply to both this patchset and the other
>> seccomp/audit patchset you posted.
>>
>> In my experience, we have two or three problems (the count varies
>> depending on perspective) when it comes to seccomp filter reporting:
>>
>> 1. Inability to log all filter actions.
>> 2. Inability to selectively enable filtering; e.g. devs want noisy
>> logging, users want relative quiet.
>> 3. Consistent behavior with audit enabled and disabled.
>
> Agreed. Those three logging issues are what have been nagging me the most.

/me nods

>> My current thinking - forgive me, this has been kicking around in my
>> head for the better part of six months (longer?) and I haven't
>> attempted to code it up - is to create a sysctl knob for a system wide
>> seccomp logging threshold that would be applied to the high 16-bits of
>> *every* triggered action: if the action was at/below the threshold a
>> record would be emitted, otherwise silence.  This should resolve
>> problems #1 and #2, and the code should be relatively straightforward
>> and small.
>
> I like that idea quite a bit. To be completely honest, for #1, I
> personally only care about logging SECCOMP_RET_ERRNO actions but this
> idea solves it in a nice and general way.

Yeah, I'd much rather solve this problem generally; everybody has
their favorite action and I'd like to avoid solving the same problem
multiple times.

Sooo ... you want to take a whack at coding this up? ;)

>> As part of the code above, I expect that all seccomp logging would get
>> routed through a single logging function (sort of like a better
>> implementation of the existing audit_seccomp()) that would check the
>> threshold and trigger the logging if needed.  This function could be
>> augmented to check for CONFIG_AUDIT and in the case where audit was
>> not built into the kernel, a simple printk could be used to log the
>> seccomp event; solving problem #3.
>
> That doesn't fully solve #3 for me. In Ubuntu (and I think Debian), we
> build with CONFIG_AUDIT enabled but don't ship auditd by default so
> audit_enabled is false. In that default configuration, we still want
> seccomp audit messages to be printk'ed. I'll need to figure out how to
> cleanly allow opting into seccomp audit messages when CONFIG_AUDIT is
> enabled and audit_enabled is false.

Heh, so you've got audit built into the kernel but you're not using
it; that sounds "fun".

Anyway, I think the logging consolidation could still help you, if for
no other reason than everything is going through the same function at
that point.  We could do some other stuff there to handle the case
where audit is compiled, but auditd is not running ... we already have
some code in place to handle that for other reasons, check
kernel/audit.c for more information.  I'd still work on the other
stuff first and then we can add this in at the end of the patchset.

>> We could also add a SECCOMP_RET_AUDIT, or similar, if we still feel
>> that is important (I personally waffle on this), but I think that is
>> independent of the ideas above.
>
> I agree that it is independent but SECCOMP_RET_AUDIT would still be
> important to Ubuntu.
>
> Tyler

-- 
paul moore
www.paul-moore.com