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

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

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.

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.

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.

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.

Thoughts?

-- 
paul moore
www.paul-moore.com