Date: Thu, 31 Jul 2025 06:07:44 -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: <CAM5tNy6Va=edwT5TTa8NEtCHrpbAnN1NMDsBKNNbqNgPoCjVng@mail.gmail.com> In-Reply-To: <CAJ5_RoDdhmpsLWtuCiaWJoR1yMvAq_4r-E%2BpUk03TiQofTZELQ@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>
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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@gmail.co= m> 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_context() A= PI that does a lot of the work of getting useful bits out of an established= 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 security con= text" (i.e., do crypto negotiation, authentication, sometimes authorization= , etc.) between two entities, the initiator and the acceprot, and then exch= anging protected messages between the two (which can be either encrypted or= just integrity protection tags for otherweise cleartext data); later exten= sions included the ability to produce identical PRF output on both parties,= etc.. The details are "mechanism-specific", and for this purpose we're ex= clusively talking about the krb5 mechanism. The steps to establish the sec= urity context are complicated and sometimes fiddly, and in the general case= can require a large number of round-trips between the initiator and accept= or before the security context is established. The individual message-prot= ection parts are comparatively simple and amendable to implementation in th= e kernel for processing efficiency. >> > RFC 2743 also defines functions for GSS_Export_sec_context() and GSS_I= mport_sec_context(), that are designed essentially to pass information abou= t an established security context from one process to another on the same m= achine (which are presumably using the same implementation and version of t= he implementation), so the contents of the exported blob are opaque and imp= lementation-specific. We are abusing that mechanism to export information = about the security context that gssd has established and feed that informat= ion into the kernel implementation of the per-message processing routines. = At present, this necessarily entails knowing the details of the implementa= tion-specific opaque blob that is the "export sec context token", which is = what the sys/kgssapi/krb5/krb5_mech.c code is doing. But if we can get the= information we want without breaking the abstraction barrier, such as via = the gss_krb5_export_lucid_sec_context() API, we are in a more robust postur= e overall and somewhat future-proofed against future evolution by MIT krb5. >> > (I note that recent Heimdal versions seem to also expose a gss_krb5_ex= port_lucid_sec_context() API, so part of the problem is just that the Heimd= al 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 the 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_external_luc= id_ctx_v1() >> function. This function only knows about the 0 and 1 setting for gctx->p= roto. >> >> Any ideas, rick >> > > > I'm not seeing anything to suggest that a "gctx->proto" value of 4 is eve= r expected; it looks like it's supposed to just be 0 (for the legacy RFC 19= 64 format) or 1 (for the "CFX" format of RFC 4121, with wider sequence numb= ers for message-protection formats, etc.). So maybe it's worth posting you= r 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, ctx, 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 data 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.) Also, if I look at the actual_mech_type returned by gss_init_sec_context(), I get an instant crash, because the "elements" pointer cannot be accessed (this doesn't much matter, since the info should always be just the Kerberos OID). --> I suspect there is some problem w.r.t. how the libraries are being buil= t? I'm now building from sources to try and dig into the library functions. rick > > From your previous message, > > > I am working on using gss_inquire_sec_context_by_oid(), which I think i= s just a front-end to gss_krb5_export_lucid_sec_context()? If that doesn't = work, I'll switch to gss_krb5_export_lucid_sec_context(). (I am still waiti= ng for the day when there is another mechanism. I have heard rumblings w.r.= t. a mechanism for the Oauth stuff, but as far as I know, about all that th= ey did was define an OID for it.) > > It looks like a front-end to the same core implementation at least (techn= ically not a wrapper for the public API, though). > (There are a bunch of non-krb5 mechanisms, most not in terribly widesprea= d use.) > > > Btw, do you have any experience porting KDC databases from Heimdal to M= IT? (At this point, Cy has done it, but after doing so, the passwords all h= ad to be reset. He thought he had used "--decrypt" when he dumped the Heimd= al KDC.) > > I do not have such experience, but the conventional way to do it involves= an unencrypted dump (which I presume is what the aforementioned "--decrypt= " does). Heimdal and MIT use (or at least used, the last time I looked) di= fferent techniques for encrypting the per-principal data in the dump file, = so a trip through plaintext helps. I do remember reading about Heimdal hav= ing grown some support for the MIT database format; the commit message at h= ttps://github.com/heimdal/heimdal/commit/57f1545a46fdad9207a71903a56f3c1d1f= ff3a10 is perhaps a very high-level description of what is expected to be p= ossible. > > -Ben
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