> 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. >> 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
