On Thu, 2024-05-02 at 14:51 -0400, Scott Mayhew wrote: > On Thu, 02 May 2024, Chuck Lever III wrote: > > > > > > > > On May 2, 2024, at 1:37 PM, Scott Mayhew <smayhew@xxxxxxxxxx> wrote: > > > > > > On Thu, 02 May 2024, Chuck Lever III wrote: > > > > > > > > On May 2, 2024, at 11:54 AM, Scott Mayhew <smayhew@xxxxxxxxxx> wrote: > > > > > > > > > > Red Hat QE identified an "interesting" issue with NFSv3 and TLS, in that an > > > > > NFSv3 client can mount with "xprtsec=none" a filesystem exported with > > > > > "xprtsec=tls:mtls" (in the sense that the client gets the filehandle and adds a > > > > > mount to its mount table - it can't actually access the mount). > > > > > > > > > > Here's an example using machines from the recent Bakeathon. > > > > > > > > > > Mounting a server with TLS enabled: > > > > > > > > > > # mount -o v4.2,sec=sys,xprtsec=tls oracle-102.chuck.lever.oracle.com.nfsv4.dev:/export/tls /mnt > > > > > # umount /mnt > > > > > > > > > > Trying to mount without "xprtsec=tls" shows that the filesystem is not exported with "xprtsec=none": > > > > > > > > > > # mount -o v4.2,sec=sys oracle-102.chuck.lever.oracle.com.nfsv4.dev:/export/tls /mnt > > > > > mount.nfs: Operation not permitted for oracle-102.chuck.lever.oracle.com.nfsv4.dev:/export/tls on /mnt > > > > > > > > > > Yet a v3 mount without "xprtsec=tls" works: > > > > > > > > > > # mount -o v3,sec=sys oracle-102.chuck.lever.oracle.com.nfsv4.dev:/export/tls /mnt > > > > > # umount /mnt > > > > > > > > > > and a mount with no explicit version and without "xprtsec=tls" falls back to > > > > > v3 and also "works": > > > > > > > > > > # mount -o sec=sys oracle-102.chuck.lever.oracle.com.nfsv4.dev:/export/tls /mnt > > > > > # grep ora /proc/mounts > > > > > oracle-102.chuck.lever.oracle.com.nfsv4.dev:/export/tls /mnt nfs > > > > > +rw,relatime,vers=3,rsize=524288,wsize=524288,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=100.64.0.49,mountvers=3,mountport=20048,mountproto=udp,local_lock=none,addr=100.64.0.49 0 0 > > > > > > > > > > Even though the filesystem is mounted, the client can't do anything with it: > > > > > > > > > > # ls /mnt > > > > > ls: cannot open directory '/mnt': Permission denied > > > > > > > > > > When krb5 is used with NFSv3, the server returns a list of pseudoflavors in > > > > > mountres3_ok (https://datatracker.ietf.org/doc/html/rfc1813#section-5.2.1). > > > > > The client compares that list with its own list of auth flavors parsed from the > > > > > mount request and returns -EACCES if no match is found (see > > > > > nfs_verify_authflavors()). > > > > > > > > > > Perhaps we should be doing something similar with xprtsec policies? > > > > > > > > The problem might be in how you've set up the exports. With NFSv3, > > > > the parent export needs the "crossmnt" export option in order for > > > > NFSv3 to behave like NFSv4 in this regard, although I could have > > > > missed something. > > > > > > I was mounting your server though :) > > > > OK, then not the same bug that Olga found last year. > > > > We should find out what FreeBSD does in this case. > > I thought about that. Rick's servers from the BAT are offline, and I > don't think he was exporting v3 anyway. > > > > > > > > > > Should > > > > > there be an errata to RFC 9289 and a request from IANA for assigned numbers for > > > > > pseudo-flavors corresponding to xprtsec policies? > > > > > > > > No. Transport-layer security is not an RPC security flavor or > > > > pseudo-flavor. These two things are not related. > > > > > > > > (And in fact, I proposed something like this for NFSv4 SECINFO, > > > > but it was rejected). > > > > > > I thought it might be a stretch to try to use mountres3.auth_flavors for > > > this, but since RFC 9289 does refer to AUTH_TLS as an authentication > > > flavor and https://www.iana.org/assignments/rpc-authentication-numbers/rpc-authentication-numbers.xhtml > > > also lists TLS under the Flavor Name column I thought it might make > > > sense to treat xprtsec policies as if they were pseudo-flavors even > > > though they're not, if only to give the client a way to determine that > > > the mount should fail. > > > > RPC_AUTH_TLS is used only when a client probes a server to see if > > it supports RPC-with-TLS. At all other times, the client uses one > > of the normal, legitimate flavors. It does not represent a security > > flavor that can be used during regular operation. > > > > NFSv3 mount failover logic is still open for discussion (ie, incomplete). > > > > Would it help if rpc.mountd stuck RPC_AUTH_TLS in the auth_flavors > > list? I think clients that don't recognize it should ignore it, > > but I'm not sure. What should a client do if it sees that flavor in > > the list? It's not one that can be used for any other procedure than > > a NULL RPC. > > Maybe? After the client gets the filehandle it's calling FSINFO and > PATHCONF. The latter get NFS3ERR_ACCES, but nfs_probe_fsinfo() isn't > checking for a negative return code from the PATHCONF operation. If it > did, it could maybe use the -EACCES coupled with the knowledge that the > server had RPC_AUTH_TLS enabled to emit an error message saying to check > the xprtsec policies (but I don't think that would be as definitive as > what I had in mind) and to fail the mount. > That sounds reasonable if it can be made to work. One could argue that to properly implement NFSv3 over TLS, that the sidecar protocols (including mountd) should be TLS-enabled as well. If that were the case, then we could just make the mount error out when the TLS handshake doesn't work. That _is_ a bit draconian though, and I don't see anyone lining up to do the mountd work anytime soon. > > > > > > > > > If not, this behavior should at least be documented in the man pages. > > > > > > > > "crossmnt", and it's kin "nohide", are explained in exports(5). > > > > > > rpc.mountd doesn't do any access checking based on xprtsec policies on > > > the export (or krb5 pseudo-flavors, for that matter), so I don't see how > > > "crossmount" or "nohide" would have any effect here. > > > > No, they don't, you are correct. > > > > > > -- > > Chuck Lever > > > > > > -- Jeffrey Layton <jlayton@xxxxxxxxxx>
