NFSv4: use mach cred for SECINFO_NO_NAME w/ integrity

Commit 97431204ea005ec8070ac94bc3251e836daa7ca7 introduced a regression
that causes SECINFO_NO_NAME to fail without sending an RPC if:

 1) the nfs_client's rpc_client is using krb5i/p (now tried by default)
 2) the current user doesn't have valid kerberos credentials

This situation is quite common - as of now a sec=sys mount would use
krb5i for the nfs_client's rpc_client and a user would hardly be faulted
for not having run kinit.

The solution is to use the machine cred when trying to use an integrity
protected auth flavor for SECINFO_NO_NAME.

Older servers may not support using the machine cred or an integrity
protected auth flavor for SECINFO_NO_NAME in every circumstance, so we fall
back to using the user's cred and the filesystem's auth flavor in this case.

We run into another problem when running against linux nfs servers -
they return NFS4ERR_WRONGSEC when using integrity auth flavor (unless the
mount is also that flavor) even though that is not a valid error for
SECINFO*.  Even though it's against spec, handle WRONGSEC errors on
SECINFO_NO_NAME by falling back to using the user cred and the
filesystem's auth flavor.

Signed-off-by: Weston Andros Adamson <dros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -7483,7 +7483,8 @@ out:
  */
 static int
 _nfs41_proc_secinfo_no_name(struct nfs_server *server, struct nfs_fh *fhandle,
-		    struct nfs_fsinfo *info, struct nfs4_secinfo_flavors *flavors)
+		    struct nfs_fsinfo *info,
+		    struct nfs4_secinfo_flavors *flavors, bool use_integrity)
 {
 	struct nfs41_secinfo_no_name_args args = {
 		.style = SECINFO_STYLE_CURRENT_FH,
@@ -7496,8 +7497,23 @@ _nfs41_proc_secinfo_no_name(struct nfs_server *server, struct nfs_fh *fhandle,
 		.rpc_argp = &args,
 		.rpc_resp = &res,
 	};
-	return nfs4_call_sync(server->nfs_client->cl_rpcclient, server, &msg,
-				&args.seq_args, &res.seq_res, 0);
+	struct rpc_clnt *clnt = server->client;
+	int status;
+
+	if (use_integrity) {
+		clnt = server->nfs_client->cl_rpcclient;
+		msg.rpc_cred = nfs4_get_clid_cred(server->nfs_client);
+	}
+
+	dprintk("--> %s\n", __func__);
+	status = nfs4_call_sync(clnt, server, &msg, &args.seq_args,
+				&res.seq_res, 0);
+	dprintk("<-- %s status=%d\n", __func__, status);
+
+	if (msg.rpc_cred)
+		put_rpccred(msg.rpc_cred);
+
+	return status;
 }
 
 static int
@@ -7507,7 +7523,24 @@ nfs41_proc_secinfo_no_name(struct nfs_server *server, struct nfs_fh *fhandle,
 	struct nfs4_exception exception = { };
 	int err;
 	do {
-		err = _nfs41_proc_secinfo_no_name(server, fhandle, info, flavors);
+		/* first try using integrity protection */
+		err = -NFS4ERR_WRONGSEC;
+
+		/* try to use integrity protection with machine cred */
+		if (_nfs4_is_integrity_protected(server->nfs_client))
+			err = _nfs41_proc_secinfo_no_name(server, fhandle, info,
+							  flavors, true);
+
+		/*
+		 * if unable to use integrity protection, or SECINFO with
+		 * integrity protection returns NFS4ERR_WRONGSEC (which is
+		 * disallowed by spec, but exists in deployed servers) use
+		 * the current filesystem's rpc_client and the user cred.
+		 */
+		if (err == -NFS4ERR_WRONGSEC)
+			err = _nfs41_proc_secinfo_no_name(server, fhandle, info,
+							  flavors, false);
+
 		switch (err) {
 		case 0:
 		case -NFS4ERR_WRONGSEC: