syscall: Test SCM credentials on Linux.

This test was previously removed in 087c6e15702e.

R=bradfitz, rsc, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/6506061

src/pkg/syscall/creds_test.go

+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build linux
+
+package syscall_test
+
+import (
+	"bytes"
+	"net"
+	"os"
+	"syscall"
+	"testing"
+)
+
+// TestSCMCredentials tests the sending and receiving of credentials
+// (PID, UID, GID) in an ancillary message between two UNIX
+// sockets. The SO_PASSCRED socket option is enabled on the sending
+// socket for this to work.
+func TestSCMCredentials(t *testing.T) {
+	fds, err := syscall.Socketpair(syscall.AF_LOCAL, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		t.Fatalf("Socketpair: %v", err)
+	}
+	defer syscall.Close(fds[0])
+	defer syscall.Close(fds[1])
+
+	err = syscall.SetsockoptInt(fds[0], syscall.SOL_SOCKET, syscall.SO_PASSCRED, 1)
+	if err != nil {
+		t.Fatalf("SetsockoptInt: %v", err)
+	}
+
+	srv, err := net.FileConn(os.NewFile(uintptr(fds[0]), ""))
+	if err != nil {
+		t.Errorf("FileConn: %v", err)
+		return
+	}
+	defer srv.Close()
+
+	cli, err := net.FileConn(os.NewFile(uintptr(fds[1]), ""))
+	if err != nil {
+		t.Errorf("FileConn: %v", err)
+		return
+	}
+	defer cli.Close()
+
+	var ucred syscall.Ucred
+	if os.Getuid() != 0 {
+		ucred.Pid = int32(os.Getpid())
+		ucred.Uid = 0
+		ucred.Gid = 0
+		oob := syscall.UnixCredentials(&ucred)
+		_, _, err := cli.(*net.UnixConn).WriteMsgUnix(nil, oob, nil)
+		if err.(*net.OpError).Err != syscall.EPERM {
+			t.Fatalf("WriteMsgUnix failed with %v, want EPERM", err)
+		}
+	}
+
+	ucred.Pid = int32(os.Getpid())
+	ucred.Uid = uint32(os.Getuid())
+	ucred.Gid = uint32(os.Getgid())
+	oob := syscall.UnixCredentials(&ucred)
+
+	// this is going to send a dummy byte
+	n, oobn, err := cli.(*net.UnixConn).WriteMsgUnix(nil, oob, nil)
+	if err != nil {
+		t.Fatalf("WriteMsgUnix: %v", err)
+	}
+	if n != 0 {
+		t.Fatalf("WriteMsgUnix n = %d, want 0", n)
+	}
+	if oobn != len(oob) {
+		t.Fatalf("WriteMsgUnix oobn = %d, want %d", oobn, len(oob))
+	}
+
+	oob2 := make([]byte, 10*len(oob))
+	n, oobn2, flags, _, err := srv.(*net.UnixConn).ReadMsgUnix(nil, oob2)
+	if err != nil {
+		t.Fatalf("ReadMsgUnix: %v", err)
+	}
+	if flags != 0 {
+		t.Fatalf("ReadMsgUnix flags = 0x%x, want 0", flags)
+	}
+	if n != 1 {
+		t.Fatalf("ReadMsgUnix n = %d, want 1 (dummy byte)", n)
+	}
+	if oobn2 != oobn {
+		// without SO_PASSCRED set on the socket, ReadMsgUnix will
+		// return zero oob bytes
+		t.Fatalf("ReadMsgUnix oobn = %d, want %d", oobn2, oobn)
+	}
+	oob2 = oob2[:oobn2]
+	if !bytes.Equal(oob, oob2) {
+		t.Fatal("ReadMsgUnix oob bytes don't match")
+	}
+
+	scm, err := syscall.ParseSocketControlMessage(oob2)
+	if err != nil {
+		t.Fatalf("ParseSocketControlMessage: %v", err)
+	}
+	newUcred, err := syscall.ParseUnixCredentials(&scm[0])
+	if err != nil {
+		t.Fatalf("ParseUnixCredentials: %v", err)
+	}
+	if *newUcred != ucred {
+		t.Fatalf("ParseUnixCredentials = %+v, want %+v", newUcred, ucred)
+	}
+}