On Tue, 2013-06-25 at 12:23 -0400, Chuck Lever wrote:
> Commit 05f4c350 "NFS: Discover NFSv4 server trunking when mounting"
> Fri Sep 14 17:24:32 2012 introduced Uniform Client String support,
> which forces our NFS client to establish a client ID immediately
> during a mount operation rather than waiting until a user wants to
> open a file.
>
> Normally machine credentials (eg. from a keytab) are used to perform
> a mount operation that is protected by Kerberos. Before 05fc350,
> SETCLIENTID used a machine credential, or fell back to a regular
> user's credential if no keytab is available.
>
> On clients that don't have a keytab, performing SETCLIENTID early
> means there's no user credential to fall back on, since no regular
> user has kinit'd yet. 05f4c350 seems to have broken the ability
> to mount with sec=krb5 on clients that don't have a keytab in
> kernels 3.7 - 3.10.
>
> To address this regression, commit 4edaa308 (NFS: Use "krb5i" to
> establish NFSv4 state whenever possible), Sat Mar 16 15:56:20 2013,
> was merged in 3.10. This commit forces the NFS client to fall back
> to AUTH_SYS for lease management operations if no keytab is
> available.
>
> Neil Brown noticed that, since root is required to kinit to do a
> sec=krb5 mount when a client doesn't have a keytab, we can try to
> use root's Kerberos credential before AUTH_SYS.
>
> Now, when determining a principal and flavor to use for lease
> management, the NFS client tries in this order:
>
> 1. Flavor: AUTH_GSS, krb5i
> Principal: service principal (via keytab)
>
> 2. Flavor: AUTH_GSS, krb5i
> Principal: user principal established for UID 0 (via kinit)
>
> 3. Flavor: AUTH_SYS
> Principal: UID 0 / GID 0
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfs/nfs4state.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
> index 1fab140..6ceece7 100644
> --- a/fs/nfs/nfs4state.c
> +++ b/fs/nfs/nfs4state.c
> @@ -154,6 +154,19 @@ struct rpc_cred *nfs4_get_machine_cred_locked(struct nfs_client *clp)
> return cred;
> }
>
> +static void nfs4_root_machine_cred(struct nfs_client *clp)
> +{
> + struct rpc_cred *cred, *new;
> +
> + new = rpc_lookup_machine_cred(NULL);
> + spin_lock(&clp->cl_lock);
> + cred = clp->cl_machine_cred;
> + clp->cl_machine_cred = new;
> + spin_unlock(&clp->cl_lock);
> + if (cred != NULL)
> + put_rpccred(cred);
> +}
> +
> static struct rpc_cred *
> nfs4_get_renew_cred_server_locked(struct nfs_server *server)
> {
> @@ -1888,9 +1901,14 @@ again:
> case -NFS4ERR_STALE_CLIENTID:
> dprintk("NFS: %s after status %d, retrying\n",
> __func__, status);
> + i = 0;
This clearly isn't resetting clp->cl_machine_cred, so how is it intended
to work?
> goto again;
> case -EACCES:
> - if (i++)
> + if (i++ == 0) {
> + nfs4_root_machine_cred(clp);
> + goto again;
> + }
> + if (i > 2)
> break;
> case -NFS4ERR_CLID_INUSE:
> case -NFS4ERR_WRONGSEC:
>
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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