net: Create client endpoint in the same dir as the remote's

With unixgram sockets, we need to specify a client endpoint, which is a
path on the filesystem with a maximum length of 104 bytes on macOS.
When using -device virtio-net,unixSocketPath=/tmp/vnet.sock, we
need to create a client endpoint before connecting to /tmp/vnet.sock.
It's currently put into `/Users/user/Library/Application Support`, which
is already fairly long. Depending on the username, the 104 bytes are
easily exceeded, this has been causing problems to podman machine.

This commit will create the client endpoint in the same directory as the
server endpoint, which gives more control to the user of vfkit wrt where
this socket is going.

This fixes crc-org#194

Signed-off-by: Christophe Fergeau <[email protected]>

pkg/vf/virtionet.go

@@ -19,20 +19,12 @@ type VirtioNet struct {
 	localAddr *net.UnixAddr
 }
 
-func localUnixSocketPath() (string, error) {
-	homeDir, err := os.UserHomeDir()
+func localUnixSocketPath(dir string) (string, error) {
+	tmpFile, err := os.CreateTemp(dir, fmt.Sprintf("vfkit-%d-*.sock", os.Getpid()))
 	if err != nil {
 		return "", err
 	}
-	dir := filepath.Join(homeDir, "Library", "Application Support", "vfkit")
-	if err := os.MkdirAll(dir, 0755); err != nil {
-		return "", err
-	}
-	tmpFile, err := os.CreateTemp(dir, fmt.Sprintf("net-%d-*.sock", os.Getpid()))
-	if err != nil {
-		return "", err
-	}
-	// slightly racy, but this is in a directory only user-writable
+	// slightly racy, but hopefully this is in a directory only user-writable
 	defer tmpFile.Close()
 	defer os.Remove(tmpFile.Name())
 
@@ -44,7 +36,7 @@ func (dev *VirtioNet) connectUnixPath() error {
 		Name: dev.UnixSocketPath,
 		Net:  "unixgram",
 	}
-	localSocketPath, err := localUnixSocketPath()
+	localSocketPath, err := localUnixSocketPath(filepath.Dir(dev.UnixSocketPath))
 	if err != nil {
 		return err
 	}

pkg/vf/virtionet_test.go

@@ -1,9 +1,6 @@
 package vf
 
 import (
-	"bytes"
-	"fmt"
-	"math/rand"
 	"net"
 	"os"
 	"path/filepath"
@@ -14,16 +11,33 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func testConnectUnixgram(t *testing.T) error {
-	unixSocketPath := filepath.Join("/tmp", fmt.Sprintf("vnet-test-%x.sock", rand.Int31n(0xffff))) //#nosec G404 -- no need for crypto/rand here
+func sourceSocketPath(t *testing.T, sourcePathLen int) (string, func()) {
+	// the 't.sock' name is chosen to be shorter than what
+	// localUnixSocketPath will generate so that the source socket path
+	// will not exceed the 104 byte limit while the destination socket path
+	// will, and will trigger an error
+	const sourceSocketName = "t.sock"
+	tmpDir := "/tmp"
+	subDirLen := sourcePathLen - len(tmpDir) - 2*len("/") - len(sourceSocketName) - 1
+	subDir := filepath.Join(tmpDir, strings.Repeat("a", subDirLen))
+	err := os.Mkdir(subDir, 0700)
+	require.NoError(t, err)
+	unixSocketPath := filepath.Join(subDir, sourceSocketName)
+	require.Equal(t, len(unixSocketPath), sourcePathLen-1)
+	return unixSocketPath, func() { os.RemoveAll(subDir) }
+
+}
+func testConnectUnixgram(t *testing.T, sourcePathLen int) error {
+	unixSocketPath, closer := sourceSocketPath(t, sourcePathLen)
+	defer closer()
+
 	addr, err := net.ResolveUnixAddr("unixgram", unixSocketPath)
 	require.NoError(t, err)
 
 	l, err := net.ListenUnixgram("unixgram", addr)
 	require.NoError(t, err)
 
 	defer l.Close()
-	defer os.Remove(unixSocketPath)
 
 	dev := &VirtioNet{
 		&config.VirtioNet{
@@ -37,46 +51,31 @@ func testConnectUnixgram(t *testing.T) error {
 
 func TestConnectUnixPath(t *testing.T) {
 	t.Run("Successful connection - no error", func(t *testing.T) {
-		err := testConnectUnixgram(t)
+		// 50 is an arbitrary number, small enough for the 104 bytes limit not to be exceeded
+		err := testConnectUnixgram(t, 50)
 		require.NoError(t, err)
 	})
 
 	t.Run("Failed connection - End socket longer than 104 bytes", func(t *testing.T) {
-		// Retrieve HOME env variable (used by the os.UserHomeDir)
-		origUserHome := os.Getenv("HOME")
-		defer func() {
-			os.Setenv("HOME", origUserHome)
-		}()
-
-		// Create a string of 100 bytes to update the user home to be sure to create a socket path > 104 bytes
-		b := bytes.Repeat([]byte("a"), 100)
-		subDir := string(b)
-
-		// Update HOME env so os.UserHomeDir returns the update path with subfolder
-		updatedUserHome := filepath.Join(origUserHome, subDir)
-		os.Setenv("HOME", updatedUserHome)
-		defer os.RemoveAll(updatedUserHome)
-
-		err := testConnectUnixgram(t)
+		err := testConnectUnixgram(t, 104)
 		// It should return an error
 		require.Error(t, err)
-		require.ErrorContains(t, err, "invalid argument")
+		require.ErrorContains(t, err, "is too long")
 	})
 }
 
 func TestLocalUnixSocketPath(t *testing.T) {
 	t.Run("Success case - Creates temporary socket path", func(t *testing.T) {
 		// Retrieve HOME env variable (used by the os.UserHomeDir)
-		userHome := os.Getenv("HOME")
+		socketDir := t.TempDir()
 
-		path, err := localUnixSocketPath()
+		path, err := localUnixSocketPath(socketDir)
 
 		// Assert successful execution
 		require.NoError(t, err)
 
 		// Check if path starts with the expected prefix
-		expectedPrefix := filepath.Join(userHome, "Library", "Application Support", "vfkit")
-		require.Truef(t, strings.HasPrefix(path, expectedPrefix), "Path doesn't start with expected prefix: %v", path)
+		require.Truef(t, strings.HasPrefix(path, socketDir), "Path doesn't start with expected prefix: %v", path)
 
 		// Check if path ends with a socket extension
 		require.Equalf(t, ".sock", filepath.Ext(path), "Path doesn't end with .sock extension: %v, ext is %v", path, filepath.Ext(path))