Date: Thu, 31 Jul 2025 07:35:07 -0700 From: Rick Macklem <rick.macklem@gmail.com> To: Benjamin Kaduk <bjkfbsd@gmail.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, Cy Schubert <Cy.Schubert@cschubert.com>, Jessica Clarke <jrtc27@freebsd.org>, Cy Schubert <cy@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@freebsd.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@freebsd.org> Subject: Re: git: c7da9fb90b0b - main - KRB5: Enable MIT KRB5 by default Message-ID: <CAM5tNy5RmoEggCjhMjLQvqMkD_7fNmxrgZGTa3hgzwn8NoCQRA@mail.gmail.com> In-Reply-To: <CAM5tNy4XupPGXHMS0p0TK0Wf_zAg5bsOzx4C1K1e-_2b=3eyUw@mail.gmail.com> References: <202507211410.56LEAD6J066633@gitrepo.freebsd.org> <47C3CC37-6F32-4376-900A-B5387B9817D5@freebsd.org> <20250721144645.3BA391BE@slippy.cwsent.com> <aH98iNXobigu39On@kib.kiev.ua> <20250722155941.AC7EB121@slippy.cwsent.com> <CAM5tNy63Ri73x3ByJUPFh7a0eCVjWPGW1hQwrkG0wz6pJ6-W3Q@mail.gmail.com> <aIcyq6JuYngAm4Ko@kib.kiev.ua> <CAM5tNy6pAUS1HD4W1=rxLXvfctAs1Ms_fxwUWz1X3tFNuVTVZg@mail.gmail.com> <CAJ5_RoBjpX_BoKgZTdOof5b83cdxjZyvn4iPM4m5voPHEr2SeQ@mail.gmail.com> <CAJ5_RoBXD4rkudaqo4BA%2BrggYcy%2BLUSnPrK2_FO4Cp_xG0fS=Q@mail.gmail.com> <CAM5tNy5DjktV54JaNcXSwc=9W9kyKTbYANyWp3wmgWu1aMvmLg@mail.gmail.com> <CAJ5_RoDdhmpsLWtuCiaWJoR1yMvAq_4r-E%2BpUk03TiQofTZELQ@mail.gmail.com> <CAM5tNy6Va=edwT5TTa8NEtCHrpbAnN1NMDsBKNNbqNgPoCjVng@mail.gmail.com> <CAM5tNy78DEgmx4z=RJbMsBkRuO6sX%2BhK9OfKbg4ACcRMnrOQgA@mail.gmail.com> <CAM5tNy4XupPGXHMS0p0TK0Wf_zAg5bsOzx4C1K1e-_2b=3eyUw@mail.gmail.com>
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On Thu, Jul 31, 2025 at 7:18=E2=80=AFAM Rick Macklem <rick.macklem@gmail.co= m> wrote: > > On Thu, Jul 31, 2025 at 6:51=E2=80=AFAM Rick Macklem <rick.macklem@gmail.= com> wrote: > > > > On Thu, Jul 31, 2025 at 6:07=E2=80=AFAM Rick Macklem <rick.macklem@gmai= l.com> wrote: > > > > > > On Wed, Jul 30, 2025 at 9:24=E2=80=AFPM Benjamin Kaduk <bjkfbsd@gmail= .com> wrote: > > > > > > > > On Wed, Jul 30, 2025 at 10:36=E2=80=AFAM Rick Macklem <rick.macklem= @gmail.com> wrote: > > > >> > > > >> On Mon, Jul 28, 2025 at 3:32=E2=80=AFPM Benjamin Kaduk <bjkfbsd@gm= ail.com> wrote: > > > >> > > > > >> > On Mon, Jul 28, 2025 at 3:04=E2=80=AFPM Benjamin Kaduk <bjkfbsd@= gmail.com> wrote: > > > >> >> > > > >> >> > > > >> >> Note that MIT krb5 provides the gss_krb5_export_lucid_sec_conte= xt() API that does a lot of the work of getting useful bits out of an estab= lished GSS security context. > > > >> >> > > > >> > > > > >> > > > > >> > > > > >> > > > > >> > And a bit more context on what is going on here and why kgssapi = has to care: > > > >> > The GSS-API (RFC 2743) is all about a way to "establish a securi= ty context" (i.e., do crypto negotiation, authentication, sometimes authori= zation, etc.) between two entities, the initiator and the acceprot, and the= n exchanging protected messages between the two (which can be either encryp= ted or just integrity protection tags for otherweise cleartext data); later= extensions included the ability to produce identical PRF output on both pa= rties, etc.. The details are "mechanism-specific", and for this purpose we= 're exclusively talking about the krb5 mechanism. The steps to establish t= he security context are complicated and sometimes fiddly, and in the genera= l case can require a large number of round-trips between the initiator and = acceptor before the security context is established. The individual messag= e-protection parts are comparatively simple and amendable to implementation= in the kernel for processing efficiency. > > > >> > RFC 2743 also defines functions for GSS_Export_sec_context() and= GSS_Import_sec_context(), that are designed essentially to pass informatio= n about an established security context from one process to another on the = same machine (which are presumably using the same implementation and versio= n of the implementation), so the contents of the exported blob are opaque a= nd implementation-specific. We are abusing that mechanism to export inform= ation about the security context that gssd has established and feed that in= formation into the kernel implementation of the per-message processing rout= ines. At present, this necessarily entails knowing the details of the impl= ementation-specific opaque blob that is the "export sec context token", whi= ch is what the sys/kgssapi/krb5/krb5_mech.c code is doing. But if we can g= et the information we want without breaking the abstraction barrier, such a= s via the gss_krb5_export_lucid_sec_context() API, we are in a more robust = posture overall and somewhat future-proofed against future evolution by MIT= krb5. > > > >> > (I note that recent Heimdal versions seem to also expose a gss_k= rb5_export_lucid_sec_context() API, so part of the problem is just that the= Heimdal in base is so old.) > > > >> > > > >> Well, here's some "not so good" news... > > > >> I've been trying to use gss_inquire_sec_context_by_oid(..) with th= e oid > > > >> for the GSS_KRB5_EXPORT_LUCID_SEC_CONTEXT_OID with version 1. > > > >> It kept failing. > > > >> The problem seems to be that "gctx->proto =3D=3D 4" in make_extern= al_lucid_ctx_v1() > > > >> function. This function only knows about the 0 and 1 setting for g= ctx->proto. > > > >> > > > >> Any ideas, rick > > > >> > > > > > > > > > > > > I'm not seeing anything to suggest that a "gctx->proto" value of 4 = is ever expected; it looks like it's supposed to just be 0 (for the legacy = RFC 1964 format) or 1 (for the "CFX" format of RFC 4121, with wider sequenc= e numbers for message-protection formats, etc.). So maybe it's worth posti= ng your current WIP somewhere to take a closer look at what's going on. > > > > > > Yea, the debugging I did was flawed (I probably got the wrong offset > > > in the structure). > > > It is weird, though. If I do gss_inquire_sec_context_by_oid(&minor, c= tx, > > > OID_FOR_GSS_INQUIRE_SSPI_SESSION_KEY, &key), it > > > works and gives me the key and encryption type. > > > > > > If I do the same, but with the 12 byte OID for LUCID v1 (the 11 bytes= from the > > > string + a 1 byte), it returns major =3D=3D GSS_S_COMPLETE, but no da= ta and > > > a weird 39756046(decimal) or 0x25ea10e(hex) minor. > > > (Oh, and I tried gss_krb5_export_lucid_sec_context() and got the same > > > weird error.) > > --> Now (after doing a "make buildworld"), gss_krb5_export_lucid_sec_co= ntext() > > returns GSS_S_BAD_MECH. Looking at the src, that error has to be f= rom > > gss_inquire_sec_context_by_oid(). So, same function fails, but a d= ifferent > > error return? > > > > It looks like "gssint_get_mechanism (ctx->mech_type)" is failing. > > I'm currently just passing GSS_C_NULL_OID into gss_init_sec_context(), > > but I've also tried the Kerberos 9 byte OID (both work, in the sense th= at > > gss_init_sec_context() seems to work, except that the actual_mech_type > > returned by it has a bogus pointer in the reply). > > --> It looks like the "mech_type" field of "ctx" is busted, for some re= ason? > > > > I'm going to try building krb5 from ports and linking to that, to see i= f it > > does the same thing. > Finally some good news... > All I did was "pkg install krb5" and then linked the gssd to the librarie= s in > /usr/local/lib and it worked!! Just to clarify, "it" refers to the gss_krb5_export_lucid_sec_context() call. I now have to debug the patch that uses it to get the kerberized NFS mounts working. rick > > Now I can test/debug the changes. > > Btw, the stuff in /usr/local/include/gssapi are correct and not messed up > like the stuff in /usr/include/gssapi. (The ones in /usr/local/include de= fine > GSS_DLLIMP for example.) > > I'm going to leave figuring out why the libraries in /usr/lib are messed = up > to someone else. > > rick > > > > > rick > > > > > > > > Also, if I look at the actual_mech_type returned by gss_init_sec_cont= ext(), > > > I get an instant crash, because the "elements" pointer cannot be > > > accessed (this doesn't much matter, since the info should always be j= ust > > > the Kerberos OID). > > > --> I suspect there is some problem w.r.t. how the libraries are bein= g built? > > > > > > I'm now building from sources to try and dig into the library functio= ns. > > > > > > rick > > > > > > > > > > > From your previous message, > > > > > > > > > I am working on using gss_inquire_sec_context_by_oid(), which I t= hink is just a front-end to gss_krb5_export_lucid_sec_context()? If that do= esn't work, I'll switch to gss_krb5_export_lucid_sec_context(). (I am still= waiting for the day when there is another mechanism. I have heard rumbling= s w.r.t. a mechanism for the Oauth stuff, but as far as I know, about all t= hat they did was define an OID for it.) > > > > > > > > It looks like a front-end to the same core implementation at least = (technically not a wrapper for the public API, though). > > > > (There are a bunch of non-krb5 mechanisms, most not in terribly wid= espread use.) > > > > > > > > > Btw, do you have any experience porting KDC databases from Heimda= l to MIT? (At this point, Cy has done it, but after doing so, the passwords= all had to be reset. He thought he had used "--decrypt" when he dumped the= Heimdal KDC.) > > > > > > > > I do not have such experience, but the conventional way to do it in= volves an unencrypted dump (which I presume is what the aforementioned "--d= ecrypt" does). Heimdal and MIT use (or at least used, the last time I look= ed) different techniques for encrypting the per-principal data in the dump = file, so a trip through plaintext helps. I do remember reading about Heimd= al having grown some support for the MIT database format; the commit messag= e at https://github.com/heimdal/heimdal/commit/57f1545a46fdad9207a71903a56f= 3c1d1fff3a10 is perhaps a very high-level description of what is expected t= o be possible. > > > > > > > > -Ben
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