Re: [PATCH v4 2/8] audit, io_uring, io-wq: add some basic audit support to io_uring
On Thu, Sep 16, 2021 at 9:33 AM Richard Guy Briggs <rgb(a)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