SUNRPC: Introduce rpc_clone_client_set_auth()

An ULP is supposed to be able to replace a GSS rpc_auth object with
another GSS rpc_auth object using rpcauth_create().  However,
rpcauth_create() in 3.5 reliably fails with -EEXIST in this case.
This is because when gss_create() attempts to create the upcall pipes,
sometimes they are already there.  For example if a pipe FS mount
event occurs, or a previous GSS flavor was in use for this rpc_clnt.

It turns out that's not the only problem here.  While working on a
fix for the above problem, we noticed that replacing an rpc_clnt's
rpc_auth is not safe, since dereferencing the cl_auth field is not
protected in any way.

So we're deprecating the ability of rpcauth_create() to switch an
rpc_clnt's security flavor during normal operation.  Instead, let's
add a fresh API that clones an rpc_clnt and gives the clone a new
flavor before it's used.

This makes immediate use of the new __rpc_clone_client() helper.

This can be used in a similar fashion to rpcauth_create() when a
client is hunting for the correct security flavor.  Instead of
replacing an rpc_clnt's security flavor in a loop, the ULP replaces
the whole rpc_clnt.

To fix the -EEXIST problem, any ULP logic that relies on replacing
an rpc_clnt's rpc_auth with rpcauth_create() must be changed to use
this API instead.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 1 insertions, 13 deletions

diff --git a/fs/nfs/nfs4namespace.c b/fs/nfs/nfs4namespace.c
index 4fdeb1b7042e..79fbb61ce202 100644
--- a/fs/nfs/nfs4namespace.c
+++ b/fs/nfs/nfs4namespace.c
@@ -192,25 +192,13 @@ out:
 struct rpc_clnt *nfs4_create_sec_client(struct rpc_clnt *clnt, struct inode *inode,
                                         struct qstr *name)
 {
-        struct rpc_clnt *clone;
-        struct rpc_auth *auth;
         rpc_authflavor_t flavor;
 
         flavor = nfs4_negotiate_security(inode, name);
         if ((int)flavor < 0)
                 return ERR_PTR((int)flavor);
 
-        clone = rpc_clone_client(clnt);
-        if (IS_ERR(clone))
-                return clone;
-
-        auth = rpcauth_create(flavor, clone);
-        if (IS_ERR(auth)) {
-                rpc_shutdown_client(clone);
-                clone = ERR_PTR(-EIO);
-        }
-
-        return clone;
+        return rpc_clone_client_set_auth(clnt, flavor);
 }
 
 static struct vfsmount *try_location(struct nfs_clone_mount *mountdata,