Re: [PATCH v1 2/2] io_uring,audit: do not log IORING_OP_*GETXATTR

[Paul Moore]

On Sat, Jan 28, 2023 at 12:26 PM Steve Grubb <sgrubb@xxxxxxxxxx> wrote:
> On Friday, January 27, 2023 5:43:02 PM EST Paul Moore wrote:
> > On Fri, Jan 27, 2023 at 12:24 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> > > Getting XATTRs is not particularly interesting security-wise.
> > >
> > > Suggested-by: Steve Grubb <sgrubb@xxxxxxxxxx>
> > > Fixes: a56834e0fafe ("io_uring: add fgetxattr and getxattr support")
> > > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > > ---
> > > io_uring/opdef.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> >
> > Depending on your security policy, fetching file data, including
> > xattrs, can be interesting from a security perspective.  As an
> > example, look at the SELinux file/getattr permission.
> >
> > https://github.com/SELinuxProject/selinux-notebook/blob/main/src/object_cla
> > sses_permissions.md#common-file-permissions
>
> We're mostly interested in setting attributes because that changes policy.
> Reading them is not interesting unless the access fails with EPERM.

See my earlier comments, SELinux does have provisions for caring about
reading xattrs, and now that I look at the rest of the LSMs it looks
like Smack cares about reading xattrs too.  Regardless of whether a
given security policy cares about xattr access, the LSMs support
enforcing access on reading xattrs so we need to ensure the audit is
setup properly in these cases.

> I was updating the user space piece recently and saw there was a bunch of
> "new" operations. I was commenting that we need to audit 5 or 6 of the "new"
> operations such as IORING_OP_MKDIRATor IORING_OP_SETXATTR. But now that I see
> the patch, it looks like they are auditable and we can just let a couple be
> skipped. IORING_OP_MADVISE is not interesting as it just gives hiints about
> the expected access patterns of memory. If there were an equivalent of
> mprotect, that would be of interest, but not madvise.

Once again, as discussed previously, it is likely that skipping
auditing for IORING_OP_MADVISE is okay, but given that several of the
changes in this patchset were incorrect, I'd like a little more
thorough investigation before we skip auditing on madvise.

> There are some I'm not sure about such as IORING_OP_MSG_RING and
> IORING_OP_URING_CMD. What do they do?

Look at 4f57f06ce218 ("io_uring: add support for IORING_OP_MSG_RING
command") for the patch which added IORING_OP_MSG_RING as it has a
decent commit description.  As for IORING_OP_URING_CMD, there were
lengthy discussions about it on the mailing lists (including audit)
back in March 2022 and then later in August on the LSM, SELinux, etc.
mailing lists when we landed some patches for it (there were no audit
changes).  I also covered the IORING_OP_URING_CMD, albeit briefly, in
a presentation at LSS-EU last year:

https://www.youtube.com/watch?v=AaaH6skUEI8
https://www.paul-moore.com/docs/2022-lss_eu-iouring_lsm-pcmoore-r3.pdf

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