Re: [PATCH v2 00/41] RPCSEC GSS krb5 enhancements

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Chuck,

On Thu, Feb 23, 2023 at 5:19 PM Chuck Lever III <chuck.lever@oracle.com> wrote:
> > On Feb 23, 2023, at 10:16 AM, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Thu, Feb 23, 2023 at 3:00 PM Chuck Lever III <chuck.lever@oracle.com> wrote:
> >>> On Feb 23, 2023, at 8:05 AM, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> >>> On Sun, 15 Jan 2023, Chuck Lever wrote:
> >>>> The purpose of this series is to improve/harden the security
> >>>> provided by the Linux kernel's RPCSEC GSS Kerberos 5 mechanism.
> >>>> There are lots of clean-ups in this series, but the pertinent
> >>>> feature is the addition of a clean deprecation path for the DES-
> >>>> and SHA1-based encryption types in accordance with Internet BCPs.
> >>>>
> >>>> This series disables DES-based enctypes by default, provides a
> >>>> mechanism for disabling SHA1-based enctypes, and introduces two
> >>>> modern enctypes that do not use deprecated crypto algorithms.
> >>>>
> >>>> Not only does that improve security for Kerberos 5 users, but it
> >>>> also prepares SunRPC for eventually switching to a shared common
> >>>> kernel Kerberos 5 implementation, which surely will not implement
> >>>> any deprecated encryption types (in particular, DES-based ones).
> >>>>
> >>>> Today, MIT supports both of the newly-introduced enctypes, but
> >>>> Heimdal does not appear to. Thus distributions can enable and
> >>>> disable kernel enctype support to match the set of enctypes
> >>>> supported in their user space Kerberos libraries.
> >>>>
> >>>> Scott has been kicking the tires -- we've found no regressions with
> >>>> the current SHA1-based enctypes, while the new ones are disabled by
> >>>> default until we have an opportunity for interop testing. The KUnit
> >>>> tests for the new enctypes pass and this implementation successfully
> >>>> interoperates with itself using these enctypes. Therefore I believe
> >>>> it to be safe to merge.
> >>>>
> >>>> When this series gets merged, the Linux NFS community should select
> >>>> and announce a date-certain for removal of SunRPC's DES-based
> >>>> enctype code.
> >>>
> >>> As this is now upstream, I gave it a try on m68k (on the ARAnyM
> >>> emulator), using a config based on atari_defconfig:
> >>>
> >>>   KTAP version 1
> >>>   # Subtest: RFC 3961 tests
> >>>   1..3
> >>>       KTAP version 1
> >>>       # Subtest: RFC 3961 n-fold
> >>>       ok 1 64-fold("012345")
> >>>       ok 2 56-fold("password")
> >>>       ok 3 64-fold("Rough Consensus, and Running Code")
> >>>       ok 4 168-fold("password")
> >>>       ok 5 192-fold("MASSACHVSETTS INSTITVTE OF TECHNOLOGY")
> >>>       ok 6 168-fold("Q")
> >>>       ok 7 168-fold("ba")
> >>>       ok 8 64-fold("kerberos")
> >>>       ok 9 128-fold("kerberos")
> >>>       ok 10 168-fold("kerberos")
> >>>       ok 11 256-fold("kerberos")
> >>>   # RFC 3961 n-fold: pass:11 fail:0 skip:0 total:11
> >>>   ok 1 RFC 3961 n-fold
> >>>       KTAP version 1
> >>>       # Subtest: RFC 3961 key derivation
> >>>   # RFC 3961 key derivation: ASSERTION FAILED at net/sunrpc/auth_gss/gss_krb5_test.c:52
> >>>   Expected gk5e != ((void *)0), but
> >>>       gk5e == 00000000
> >>>       ((void *)0) == 00000000
> >>>       not ok 1 des3-hmac-sha1 key derivation case 1
> >>
> >> Geert, thanks for testing GSS on m68k.
> >>
> >> This assertion failure means that support for the encryption types
> >> specified in RFC 3961 is not built into your kernel.
> >>
> >> The new Kunit tests don't work unless everything is built in --
> >>
> >> there's a net/sunrpc/.kunitconfig that provides the supported
> >> build configuration for running them. I typically use a command
> >> line similar to this:
> >>
> >> ./tools/testing/kunit/kunit.py run --raw_output=all --kunitconfig ./net/sunrpc/.kunitconfig
> >
> > Aren't modular crypto algorithms auto-loaded when needed?
>
> The ciphers and digests are handled via the kernel's crypto
> manager. They will indeed get auto-loaded by SunRPC's GSS on
> demand, but of course, the set of algorithms used by GSS
> has to be enabled by Kconfig options first.
>
> SunRPC GSS has a set of Kerberos encryption types that make
> use of individual ciphers and digests. Those have never been
> modularized, and they are each enabled by Kconfig options,
> as explained below.
>
>
> > In general, it's a good idea to make the tests test only functionality
> > that is available, either through "depends on" in Kconfig, or "#if
> > IS_ENABLED(...)".
>
> An earlier version of this patch set did just that. It became
> quite a mess. That's why I chose the .kunitconfig approach.
>
>
> > Of course that does not preclude providing a
> > .kunitconfig to enable and test everything.
>
> The suite should test every Kerberos encryption type that
> SunRPC GSS has support for. There's no reason to disable a
> particular encryption type when running the unit tests...
> unless I'm missing something?

That depends: do you want to test everything, or do you want to test
(only) the functionality you enabled for your product?
I tend to enable all modular tests, so I can use insmod to run any
relevant test when needed.  If a test suddenly needs something that
is not enabled, you can not run the test without enabling extra
functionality (which you may not want to enable).

> > Note that net/sunrpc/.kunitconfig has
> >
> >    CONFIG_RPCSEC_GSS_KRB5_KUNIT_TEST=y
> >
> > which needs KUNIT_ALL_TESTS=y, else it will still be modular.
> >
> > First, I tried getting my modular setup working.
> > After enabling:
> >    CONFIG_RPCSEC_GSS_KRB5_ENCTYPES_DES=y
>
> And CONFIG_RPCSEC_GSS_KRB5_ENCTYPES_AES_SHA1=y ??

Sure, I had that enabled, thanks to "default y".

> > Third, with net/sunrpc/.kunitconfig, and
> > CONFIG_RPCSEC_GSS_KRB5_KUNIT_TEST=y:

[...]

> > Unable to handle kernel access at virtual address af06da84

> > I.e. a slightly different crash.
> > As the difference between the two crashes is modular vs. builtin,
> > this looks like an out-of-bound access in the test.
>
> Why not run the test suite just as I suggested?

I don't think I can use tools/testing/kunit/kunit.py to run the tests
when cross-compiling my kernel?

My third case (adding options from net/sunrpc/.kunitconfig, and
setting CONFIG_RPCSEC_GSS_KRB5_KUNIT_TEST=y) should be equivalent to
that, right?

> Since I cannot reproduce this crash and do not have an m68k
> platform available to me, I will need you to continue to
> pursue the issue. I'll help as much as I can.
>
> I would very much like to see successful test results on
> non-x86 platforms.

Thanks, I'll give it a try on some other platforms, later...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds