Re: [PATCH 28/32] selinux: Use mem_to_flex_dup() with xfrm and sidtab

Paul Moore
2022-05-05T23:16:31Z

On Thu, May 5, 2022 at 2:39 PM Kees Cook <keescook@chromium.org> wrote:
> On Wed, May 04, 2022 at 11:14:42PM -0400, Paul Moore wrote:
> > On Wed, May 4, 2022 at 7:34 PM Gustavo A. R. Silva
> > <gustavoars@kernel.org> wrote:
> > >
> > > Hi Paul,
> > >
> > > On Wed, May 04, 2022 at 06:57:28PM -0400, Paul Moore wrote:
> > > > On Tue, May 3, 2022 at 9:57 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > [..]
> > >
> > > > > +++ b/include/uapi/linux/xfrm.h
> > > > > @@ -31,9 +31,9 @@ struct xfrm_id {
> > > > > struct xfrm_sec_ctx {
> > > > > __u8 ctx_doi;
> > > > > __u8 ctx_alg;
> > > > > - __u16 ctx_len;
> > > > > + __DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(__u16, ctx_len);
> > > > > __u32 ctx_sid;
> > > > > - char ctx_str[0];
> > > > > + __DECLARE_FLEX_ARRAY_ELEMENTS(char, ctx_str);
> > > > > };
> > > >
> > > > While I like the idea of this in principle, I'd like to hear about the
> > > > testing you've done on these patches. A previous flex array
> > > > conversion in the audit uapi headers ended up causing a problem with
> > >
> > > I'm curious about which commit caused those problems...?
> >
> > Commit ed98ea2128b6 ("audit: replace zero-length array with
> > flexible-array member"), however, as I said earlier, the problem was
> > actually with SWIG, it just happened to be triggered by the kernel
> > commit. There was a brief fedora-devel mail thread about the problem,
> > see the link below:
> >
> > * https://www.spinics.net/lists/fedora-devel/msg297991.html
>
> Wow, that's pretty weird -- it looks like SWIG was scraping the headers
> to build its conversions? I assume SWIG has been fixed now?

I honestly don't know, the audit userspace was hacking around it with
some header file duplication/munging last I heard, but I try to avoid
having to touch Steve's audit userspace code.

> > To reiterate, I'm supportive of changes like this, but I would like to
> > hear how it was tested to ensure there are no unexpected problems with
> > userspace. If there are userspace problems it doesn't mean we can't
> > make changes like this, it just means we need to ensure that the
> > userspace issues are resolved first.
>
> Well, as this is the first and only report of any problems with [0] -> []
> conversions (in UAPI or anywhere) that I remember seeing, and they've
> been underway since at least v5.9, I hadn't been doing any new testing.

... and for whatever it is worth, I wasn't expecting it to be a
problem either. Surprise :)

> So, for this case, I guess I should ask what tests you think would be
> meaningful here? Anything using #include should be fine:
> https://codesearch.debian.net/search?q=linux%2Fxfrm.h&literal=1&perpkg=1
> Which leaves just this, which may be doing something weird:
>
> libabigail_2.0-1/tests/data/test-diff-filter/test-PR27569-v0.abi
> </data-member>
> <data-member access="public" layout-offset-in-bits="128">
> <var-decl name="seq_hi" type-id="3f1a6b60" visibility="default" filepath="include/uapi/linux/xfrm.h" line="97" column="1"/>
> </data-member>
> <data-member access="public" layout-offset-in-bits="160">
>
> But I see that SWIG doesn't show up in a search for linux/audit.h:
> https://codesearch.debian.net/search?q=linux%2Faudit.h&literal=1&perpkg=1
>
> So this may not be a sufficient analysis...

I think from a practical perspective ensuring that the major IPsec/IKE
tools, e.g. the various *SWANs, that know about labeled IPSec still
build and can set/get the SA/SPD labels correctly would be sufficient.
I seriously doubt there would be any problems, but who knows.

--
paul-moore.com