cnci-agent: Read entropy from /dev/urandom directly

This commit reverts to the previous Go 1.8 behaviour in which the TLS
session started by ssntp.Dial received its entropy by reading from
/dev/urandom directly.  The default behaviour has changed in Go 1.9
to retrieve random data by calling getrandom without the non block
flag.  Getrandom will therefore block if the urandom pool is not
initialised which can easily happen when a VM boots for the first time
like a CNCI.

Fixes: #1408

Signed-off-by: Mark Ryan <mark.d.ryan@intel.com>

networking/ciao-cnci-agent/client.go

@@ -19,6 +19,7 @@ package main
 import (
 	"encoding/json"
 	"flag"
+	"io"
 	"io/ioutil"
 	"log"
 	"os"
@@ -67,6 +68,8 @@ const (
 	interfacesDir = "/var/lib/ciao/network/interfaces"
 )
 
+var cnciRand io.Reader
+
 type cmdWrapper struct {
 	cmd interface{}
 }
@@ -349,7 +352,7 @@ func connectToServer(db *cnciDatabase, doneCh chan struct{}, statusCh chan struc
 	}()
 
 	cfg := &ssntp.Config{UUID: agentUUID, URI: serverURL, CAcert: serverCertPath, Cert: clientCertPath,
-		Log: ssntp.Log}
+		Log: ssntp.Log, Rand: cnciRand}
 	client := &agentClient{db: db, cmdCh: make(chan *cmdWrapper)}
 
 	dialCh := make(chan error)

networking/ciao-cnci-agent/rand_linux.go

@@ -0,0 +1,54 @@
+//
+// Copyright (c) 2016 Intel Corporation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+package main
+
+import (
+	"bufio"
+	"io"
+	"os"
+	"sync"
+	"syscall"
+)
+
+type nbRandReader struct {
+	f    io.Reader
+	lock sync.Mutex
+}
+
+func (r *nbRandReader) Read(p []byte) (int, error) {
+	r.lock.Lock()
+	n, err := r.f.Read(p)
+	r.lock.Unlock()
+	if re, ok := err.(*os.PathError); ok {
+		if re, ok := re.Err.(syscall.Errno); ok {
+			if re == syscall.EAGAIN {
+				err = nil
+			}
+		}
+	}
+
+	return n, err
+}
+
+func init() {
+	r, err := os.Open("/dev/urandom")
+	if err != nil {
+		return
+	}
+
+	cnciRand = &nbRandReader{f: bufio.NewReader(r)}
+}