On Tue, 30 Jul 2013 15:58:18 +0200
Marcus Moeller <marcus.moeller@xxxxxx> wrote:
> Hi again,
>
> >>>>>>> On Mon, 29 Jul 2013 14:50:03 +0200
> >>>>>>> Marcus Moeller <marcus.moeller@xxxxxx> wrote:
> >>>>>>>
> >>>>>>>> [ 124.607810] fs/cifs/cifssmb.c: negprot rc 0
> >>>>>>>> [ 124.607814] fs/cifs/connect.c: Security Mode: 0xf Capabilities:
> >>>>>>>> 0x8001f3fc TimeAdjust: -7200
> >>>>>>>> [ 124.607817] fs/cifs/sess.c: sess setup type 4
> >>>>>>>> [ 124.607826] fs/cifs/cifs_spnego.c: key description =
> >>>>>>>> ver=0x2;host=d.ethz.ch;ip4=82.130.70.6;sec=krb5;uid=0xaf05;creduid=0xaf05;user=mam4tst;pid=0x61a
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> [ 124.803185] fs/cifs/sess.c: ssetup freeing small buf
> >>>>>>>> ffff88022c31a000
> >>>>>>>> [ 124.803195] CIFS VFS: Send error in SessSetup = -126
> >>>>>>>> [ 124.803203] fs/cifs/connect.c: CIFS VFS: leaving
> >>>>>>>> cifs_get_smb_ses (xid = 5) rc = -126
> >>>>>>>> [ 124.803212] fs/cifs/fscache.c:
> >>>>>>>> cifs_fscache_release_client_cookie:
> >>>>>>>> (0xffff88022a1b6000/0xffff88022a6430f0)
> >>>>>>>> [ 124.803368] fs/cifs/connect.c: CIFS VFS: leaving cifs_mount (xid
> >>>>>>>> = 4) rc = -126
> >>>>>>>> [ 124.803374] CIFS VFS: cifs_mount failed w/return code = -126
> >>>>>>>
> >>>>>>> The only failure I see is the one above, and that's because it failed
> >>>>>>> to upcall for the correct key. Are you sure you have krb5 creds as
> >>>>>>> that
> >>>>>>> user?
> >>>>>>
> >>>>>> Yes, creds are there and it also works when mounting from one of the
> >>>>>> servers directly.
> >>>>>>
> >>>>>> Only mounting using the domainname does not work.
> >>>>>>
> >>>>>>
> >>>>>>>> [ 131.324798] fs/cifs/cifssmb.c: negprot rc 0
> >>>>>>>> [ 131.324804] fs/cifs/connect.c: Security Mode: 0xf Capabilities:
> >>>>>>>> 0x8001f3fc TimeAdjust: -7200
> >>>>>>>> [ 131.324808] fs/cifs/sess.c: sess setup type 4
> >>>>>>>> [ 131.324821] fs/cifs/cifs_spnego.c: key description =
> >>>>>>>> ver=0x2;host=d.ethz.ch;ip4=172.31.65.62;sec=krb5;uid=0xaf05;creduid=0xaf05;user=mam4tst;pid=0x62c
> >>
> >>>>>>>> [ 131.384335] fs/cifs/transport.c: For smb_command 115
> >>>>>>>> [ 131.384344] fs/cifs/transport.c: Sending smb: smb_len=1666
> >>>>>>>> [ 131.387043] fs/cifs/connect.c: RFC1002 header 0xf9
> >>>>>>>> [ 131.387055] fs/cifs/misc.c: checkSMB Length: 0xfd,
> >>>>>>>> smb_buf_length: 0xf9
> >>>>>>>> [ 131.387095] fs/cifs/transport.c: cifs_sync_mid_result: cmd=115
> >>>>>>>> mid=2 state=4
> >>>>>>>> [ 131.387100] fs/cifs/misc.c: Null buffer passed to
> >>>>>>>> cifs_small_buf_release
> >>>>>>>
> >>>>>>> Here' the upcall for a similar set of creds worked fine. The only
> >>>>>>> thing
> >>>>>>> that seems to have changed in the key description is the IP address.
> >>>>>>>
> >>>>>>> Do you have cifs.upcall set up to use the --trust-dns flag? If so,
> >>>>>>> why?
> >>>>>>
> >>>>>> A relict from the past. I have removed it from the config. Thanks for
> >>>>>> pointing out.
> >>
> >> Sorry, I was wrong. Without the -t option I am not even able to mount it
> >> at all. The man page states a few words on that parameter, but I am
> >> still not sure how it works when -t is not set.
> >>
> >> With -t set, the initial problem with the domain lookup works, when
> >> reverse DNS is configured propably.
> >>
> >
> > Ok, that makes sense then. The problem here is that the kernel needs to
> > know what service principal name to use when contacting the server, and
> > I suspect your krb5 configuration is not quite right.
> >
> > It looks like you're doing something like:
> >
> > mount //d.ethz.ch/dfs /mnt/dfs -o sec=krb5...
> >
> > ...at this point, what happens is that the kernel needs to get a krb5
> > service ticket to talk to the CIFS service on the host.
> >
> > What it typically does is take the hostname in the UNC that you're
> > trying to mount, prepend it with "cifs/" and then try to get a service
> > ticket for that. In your case, it'll look something like this:
> >
> > cifs/d.ethz.ch@xxxxxxxxxxxxxxxxxxxxxx
> >
> > ...now, typically if that fails, we'll give up. Trying to do anything
> > else is not considered safe since it's vulernable to DNS spoofing.
> >
> > If however, you add the '-t' flag to cifs.upcall, that tells it to try
> > and guess the hostname part of that principal by reverse resolving it in
> > DNS. It takes the IP address to which you are connecting, does a
> > reverse DNS lookup and then uses that in the SPN.
> >
> > This is less safe, since if your DNS server is compromised someone
> > could redirect you to a malicious server, and your client wouldn't be
> > able to trivially detect that. So it in effect waters down krb5
> > security.
> >
> > The correct fix is to ensure that the server(s) to which you are
> > connecting have the ability to accept SPNs for the "hostnames" to which
> > you want to connect. That means that you need to add SPNs for
> > cifs/d.ethz.ch and ensure that the server will accept them to talk to
> > its cifs service.
> >
> > Alternately, you can continue to use the '-t' flag and ensure that each
> > possible server accepts principals for the hostnames to which their IP
> > addresses reverse-resolve, with the caveat that its less safe than
> > doing that the "right way".
> >
> > As to how to add these principals and make the server accept them...it
> > depends on the server.
> >
> > Clear as mud?
>
> Hehe, thanks for pointing that out. One thing I am not yet aware of is
> where the SPN cifs/d.ethz.ch has to be set? On the DFS Servers and/or on
> the servers which hold the shares? The latter ones are EMC and the DFS
> Servers are 2008R2.
>
> Greets
> Marcus
>
Definitely on the first DFS server. On the others, they'll need to
accept SPNs holding the hostnames that are in the DFS referrals. So if
your DFS server gives you a referral that's something like this:
bar -> //foo.d.ethz.ch/bar
...then you'll need to ensure that foo.d.ethz.ch accepts SPNs that have
that hostname in them.
--
Jeff Layton <jlayton@xxxxxxxxxx>
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