linux-kernel - Re: [PATCH 0/2] Begin auditing SECCOMP_RET

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Message-ID: <8748cee7-efe3-a603-ef2e-dc9077b6ead4@canonical.com>
Date:   Tue, 3 Jan 2017 07:31:16 -0600
From:   Tyler Hicks <tyhicks@...onical.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Eric Paris <eparis@...hat.com>, Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, linux-audit@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Begin auditing SECCOMP_RET_ERRNO return actions

On 01/02/2017 04:47 PM, Paul Moore wrote:
> On Mon, Jan 2, 2017 at 11:53 AM, Tyler Hicks <tyhicks@...onical.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.

> 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.

> 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.

> 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



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