Re: [PATCH] selinux: add __randomize_layout to selinux_audit_data

[Paul Moore]

On Wed, May 18, 2022 at 2:53 AM Gong Ruiqi <gongruiqi1@xxxxxxxxxx> wrote:
> On 2022/05/18 9:39, Paul Moore wrote:
> > On Tue, May 17, 2022 at 9:21 PM GONG, Ruiqi <gongruiqi1@xxxxxxxxxx> wrote:
> >>
> >> Randomize the layout of struct selinux_audit_data as suggested in [1],
> >> since it contains a pointer to struct selinux_state, an already
> >> randomized strucure.
> >>
> >> [1]: https://github.com/KSPP/linux/issues/188
> >>
> >> Signed-off-by: GONG, Ruiqi <gongruiqi1@xxxxxxxxxx>
> >> ---
> >>  security/selinux/include/avc.h | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
> >> index 2b372f98f2d7..5525b94fd266 100644
> >> --- a/security/selinux/include/avc.h
> >> +++ b/security/selinux/include/avc.h
> >> @@ -53,7 +53,7 @@ struct selinux_audit_data {
> >>         u32 denied;
> >>         int result;
> >>         struct selinux_state *state;
> >> -};
> >> +} __randomize_layout;
> >
> > I'll apologize in advance for the stupid question, but does
>
> Not at all :)
>
> > __randomize_layout result in any problems when the struct is used in a
> > trace event?  (see include/trace/events/avc.h)
>
> No, as least it doesn't in the testing I did. I believe we can use the
> struct tagged with __randomize_layout as normal except that 1) it should
> be initialized with a designated initializer, and 2) pointers to this
> type can't be cast to/from pointers to another type. Other operations
> like dereferencing members of the struct (as in
> include/trace/events/avc.h) shouldn't be a problem.
>
> I did a testing to the patch on a qemu vm by running the selinux
> testsuite with tracing events "avc:selinux_audited" enabled. The
> testsuite completed successfully and from the tracing log I saw nothing
> abnormal with my bare eyes. You can do more testing if you want or you
> have other ideas of how to do so ;)

That's great, thanks for verifying this.  I was aware of the other
restrictions but wasn't sure about tracing.  Now I know :)

It's too late to go into selinux/next for this dev cycle, but I'll
queue this up for selinux/next once the merge window closes.

Thanks again!

-- 
paul-moore.com