[PATCH v4 2/8] audit, io_uring, io-wq: add some basic audit support to io_uring

[Paul Moore]

On Thu, Sep 16, 2021 at 9:33 AM Richard Guy Briggs <rgb at redhat.com> wrote:
> On 2021-09-15 12:49, Paul Moore wrote:
> > This patch adds basic auditing to io_uring operations, regardless of
> > their context.  This is accomplished by allocating audit_context
> > structures for the io-wq worker and io_uring SQPOLL kernel threads
> > as well as explicitly auditing the io_uring operations in
> > io_issue_sqe().  Individual io_uring operations can bypass auditing
> > through the "audit_skip" field in the struct io_op_def definition for
> > the operation; although great care must be taken so that security
> > relevant io_uring operations do not bypass auditing; please contact
> > the audit mailing list (see the MAINTAINERS file) with any questions.
> >
> > The io_uring operations are audited using a new AUDIT_URINGOP record,
> > an example is shown below:
> >
> >   type=UNKNOWN[1336] msg=audit(1630523381.288:260):
> >     uring_op=19 success=yes exit=0 items=0 ppid=853 pid=1204
> >     uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0
> >     subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
> >     key=(null)
> >     AUID="root" UID="root" GID="root" EUID="root" SUID="root"
> >     FSUID="root" EGID="root" SGID="root" FSGID="root"
> >
> > Thanks to Richard Guy Briggs for review and feedback.
>
> I share Steve's concerns about the missing auid and ses.  The userspace
> log interpreter conjured up AUID="root" from the absent auid=.
>
> Some of the creds are here including ppid, pid, a herd of *id and subj.
> *Something* initiated this action and then delegated it to iouring to
> carry out.  That should be in there somewhere.  You had a concern about
> shared queues and mis-attribution.  All of these creds including auid
> and ses should be kept together to get this right.

Look, there are a lot of things about io_uring that frustrate me from
a security perspective - this is one of them - but I've run out of
ways to say it's not possible to reliably capture the audit ID or
session ID here.  With io_uring it is possible to submit an io_uring
operation, and capture the results, by simply reading and writing to a
mmap'd buffer.  Yes, it would be nice to have that information, but I
don't believe there is a practical way to capture it.  If you have any
suggestions on how to do so, please share, but please make it
concrete; hand wavy solutions aren't useful at this stage.

As for the userspace mysteriously creating an AUID out of thin air,
that was my mistake: I simply removed the "auid=" field from the
example and didn't remove the additional fields, e.g. AUID, that
auditd appends to the end of the record.  I've updated the commit
description with a freshly generated record and removed the auditd
bonus bits as those probably shouldn't be shown in an example of a
kernel generated audit record.  I'm not going to repost the patchset
just for this small edit to the description, but I have force-pushed
the update to the selinux/working-io_uring branch.

-- 
paul moore
www.paul-moore.com