azure: Don't exec 'cat' to read files.

pkg/volume/azure_dd/azure_common.go

@@ -21,7 +21,6 @@ import (
 	"io/ioutil"
 	"os"
 	"path"
-	"regexp"
 	"strconv"
 	libstrings "strings"
 
@@ -158,6 +157,7 @@ type ioHandler interface {
 	ReadDir(dirname string) ([]os.FileInfo, error)
 	WriteFile(filename string, data []byte, perm os.FileMode) error
 	Readlink(name string) (string, error)
+	ReadFile(filename string) ([]byte, error)
 }
 
 //TODO: check if priming the iscsi interface is actually needed
@@ -176,6 +176,10 @@ func (handler *osIOHandler) Readlink(name string) (string, error) {
 	return os.Readlink(name)
 }
 
+func (handler *osIOHandler) ReadFile(filename string) ([]byte, error) {
+	return ioutil.ReadFile(filename)
+}
+
 // exclude those used by azure as resource and OS root in /dev/disk/azure
 func listAzureDiskPath(io ioHandler) []string {
 	azureDiskPath := "/dev/disk/azure/"
@@ -237,18 +241,30 @@ func findDiskByLunWithConstraint(lun int, io ioHandler, exe exec.Interface, azur
 			if lun == l {
 				// find the matching LUN
 				// read vendor and model to ensure it is a VHD disk
-				vendor := path.Join(sys_path, name, "vendor")
-				model := path.Join(sys_path, name, "model")
-				out, err := exe.Command("cat", vendor, model).CombinedOutput()
+				vendorPath := path.Join(sys_path, name, "vendor")
+				vendorBytes, err := io.ReadFile(vendorPath)
 				if err != nil {
-					glog.V(4).Infof("azure disk - failed to cat device vendor and model, err: %v", err)
+					glog.Errorf("failed to read device vendor, err: %v", err)
 					continue
 				}
-				matched, err := regexp.MatchString("^MSFT[ ]{0,}\nVIRTUAL DISK[ ]{0,}\n$", libstrings.ToUpper(string(out)))
-				if err != nil || !matched {
-					glog.V(4).Infof("azure disk - doesn't match VHD, output %v, error %v", string(out), err)
+				vendor := libstrings.TrimSpace(string(vendorBytes))
+				if libstrings.ToUpper(vendor) != "MSFT" {
+					glog.V(4).Infof("vendor doesn't match VHD, got %s", vendor)
 					continue
 				}
+
+				modelPath := path.Join(sys_path, name, "model")
+				modelBytes, err := io.ReadFile(modelPath)
+				if err != nil {
+					glog.Errorf("failed to read device model, err: %v", err)
+					continue
+				}
+				model := libstrings.TrimSpace(string(modelBytes))
+				if libstrings.ToUpper(model) != "VIRTUAL DISK" {
+					glog.V(4).Infof("model doesn't match VHD, got %s", model)
+					continue
+				}
+
 				// find a disk, validate name
 				dir := path.Join(sys_path, name, "block")
 				if dev, err := io.ReadDir(dir); err == nil {

pkg/volume/azure_dd/azure_common_test.go

@@ -19,6 +19,7 @@ package azure_dd
 import (
 	"fmt"
 	"os"
+	"strings"
 	"testing"
 	"time"
 
@@ -107,6 +108,16 @@ func (handler *fakeIOHandler) Readlink(name string) (string, error) {
 	return "/dev/azure/disk/sda", nil
 }
 
+func (handler *fakeIOHandler) ReadFile(filename string) ([]byte, error) {
+	if strings.HasSuffix(filename, "vendor") {
+		return []byte("Msft    \n"), nil
+	}
+	if strings.HasSuffix(filename, "model") {
+		return []byte("Virtual Disk \n"), nil
+	}
+	return nil, fmt.Errorf("unknown file")
+}
+
 func TestIoHandler(t *testing.T) {
 	var fcmd fakeexec.FakeCmd
 	fcmd = fakeexec.FakeCmd{