On Mon, 07 Oct 2024, Chuck Lever III wrote: > > > > On Oct 6, 2024, at 6:29 PM, Pali Rohár <pali@xxxxxxxxxx> wrote: > > > > On Monday 07 October 2024 09:13:17 NeilBrown wrote: > >> On Mon, 07 Oct 2024, Chuck Lever wrote: > >>> On Fri, Sep 13, 2024 at 08:52:20AM +1000, NeilBrown wrote: > >>>> On Fri, 13 Sep 2024, Pali Rohár wrote: > >>>>> Currently NFSD_MAY_BYPASS_GSS and NFSD_MAY_BYPASS_GSS_ON_ROOT do not bypass > >>>>> only GSS, but bypass any authentication method. This is problem specially > >>>>> for NFS3 AUTH_NULL-only exports. > >>>>> > >>>>> The purpose of NFSD_MAY_BYPASS_GSS_ON_ROOT is described in RFC 2623, > >>>>> section 2.3.2, to allow mounting NFS2/3 GSS-only export without > >>>>> authentication. So few procedures which do not expose security risk used > >>>>> during mount time can be called also with AUTH_NONE or AUTH_SYS, to allow > >>>>> client mount operation to finish successfully. > >>>>> > >>>>> The problem with current implementation is that for AUTH_NULL-only exports, > >>>>> the NFSD_MAY_BYPASS_GSS_ON_ROOT is active also for NFS3 AUTH_UNIX mount > >>>>> attempts which confuse NFS3 clients, and make them think that AUTH_UNIX is > >>>>> enabled and is working. Linux NFS3 client never switches from AUTH_UNIX to > >>>>> AUTH_NONE on active mount, which makes the mount inaccessible. > >>>>> > >>>>> Fix the NFSD_MAY_BYPASS_GSS and NFSD_MAY_BYPASS_GSS_ON_ROOT implementation > >>>>> and really allow to bypass only exports which have some GSS auth flavor > >>>>> enabled. > >>>>> > >>>>> The result would be: For AUTH_NULL-only export if client attempts to do > >>>>> mount with AUTH_UNIX flavor then it will receive access errors, which > >>>>> instruct client that AUTH_UNIX flavor is not usable and will either try > >>>>> other auth flavor (AUTH_NULL if enabled) or fails mount procedure. > >>>>> > >>>>> This should fix problems with AUTH_NULL-only or AUTH_UNIX-only exports if > >>>>> client attempts to mount it with other auth flavor (e.g. with AUTH_NULL for > >>>>> AUTH_UNIX-only export, or with AUTH_UNIX for AUTH_NULL-only export). > >>>> > >>>> The MAY_BYPASS_GSS flag currently also bypasses TLS restrictions. With > >>>> your change it doesn't. I don't think we want to make that change. > >>> > >>> Neil, I'm not seeing this, I must be missing something. > >>> > >>> RPC_AUTH_TLS is used only on NULL procedures. > >>> > >>> The export's xprtsec= setting determines whether a TLS session must > >>> be present to access the files on the export. If the TLS session > >>> meets the xprtsec= policy, then the normal user authentication > >>> settings apply. In other words, I don't think execution gets close > >>> to check_nfsd_access() unless the xprtsec policy setting is met. > >> > >> check_nfsd_access() is literally the ONLY place that ->ex_xprtsec_modes > >> is tested and that seems to be where xprtsec= export settings are stored. > >> > >>> > >>> I'm not convinced check_nfsd_access() needs to care about > >>> RPC_AUTH_TLS. Can you expand a little on your concern? > >> > >> Probably it doesn't care about RPC_AUTH_TLS which as you say is only > >> used on NULL procedures when setting up the TLS connection. > >> > >> But it *does* care about NFS_XPRTSEC_MTLS etc. > >> > >> But I now see that RPC_AUTH_TLS is never reported by OP_SECINFO as an > >> acceptable flavour, so the client cannot dynamically determine that TLS > >> is required. > > > > Why is not RPC_AUTH_TLS announced in NFS4 OP_SECINFO? Should not NFS4 > > OP_SECINFO report all possible auth methods for particular filehandle? > > SECINFO reports user authentication flavors and pseudoflavors. > > RPC_AUTH_TLS is not a user authentication flavor, it is merely > a query to see if the server peer supports RPC-with-TLS. > > So far the nfsv4 WG has not been able to come to consensus > about how a server's transport layer security policies should > be reported to clients. There does not seem to be a clean way > to do that with existing NFSv4 protocol elements, so a > protocol extension might be needed. Interesting... The distinction between RPC_AUTH_GSS_KRB5I and RPC_AUTH_GSS_KRB5P is not about user authentication, it is about transport privacy. And the distinction between xprtsec=tls and xprtsec=mtls seems to be precisely about user authentication. I would describe the current pseudo flavours as not "a clean way" to advise the client of security requirements, but they are at least established practice. RPC_AUTH_SYS_TLS seems to me to be an obvious sort of pseudo flavour. But I suspect all these arguments and more have already been discussed within the working group and people can sensibly have different opinions. Thanks for helping me understand NFS/TLS a bit better. NeilBrown > > > >> So there is no value in giving non-tls clients access to > >> xprtsec=mtls exports so they can discover that for themselves. The > >> client needs to explicitly mount with tls, or possibly the client can > >> opportunistically try TLS in every case, and call back. > >> > >> So the original patch is OK. > >> > >> NeilBrown > > > -- > Chuck Lever > > >
