os, syscall: fix incorrect offset calculation in Readlink on windows

Current implementation of syscall.Readlink mistakenly calculates
the end offset of the PrintName field.
Also, there are some cases that the PrintName field is empty.
Instead, the CL uses SubstituteName with correct calculation.

Fixes #15978
Fixes #16145

Change-Id: If3257137141129ac1c552d003726d5b9c08bb754
Reviewed-on: https://go-review.googlesource.com/31118
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

5 files changed, 153 insertions, 4 deletions

diff --git a/src/internal/syscall/windows/syscall_windows.go b/src/internal/syscall/windows/syscall_windows.go
index 4a30afbbfc..dd2df92ff6 100644
--- a/src/internal/syscall/windows/syscall_windows.go
+++ b/src/internal/syscall/windows/syscall_windows.go
@@ -148,3 +148,19 @@ const MB_ERR_INVALID_CHARS = 8
 //sys	GetConsoleCP() (ccp uint32) = kernel32.GetConsoleCP
 //sys	MultiByteToWideChar(codePage uint32, dwFlags uint32, str *byte, nstr int32, wchar *uint16, nwchar int32) (nwrite int32, err error) = kernel32.MultiByteToWideChar
 //sys	GetCurrentThread() (pseudoHandle syscall.Handle, err error) = kernel32.GetCurrentThread
+
+const STYPE_DISKTREE = 0x00
+
+type SHARE_INFO_2 struct {
+	Netname     *uint16
+	Type        uint32
+	Remark      *uint16
+	Permissions uint32
+	MaxUses     uint32
+	CurrentUses uint32
+	Path        *uint16
+	Passwd      *uint16
+}
+
+//sys  NetShareAdd(serverName *uint16, level uint32, buf *byte, parmErr *uint16) (neterr error) = netapi32.NetShareAdd
+//sys  NetShareDel(serverName *uint16, netName *uint16, reserved uint32) (neterr error) = netapi32.NetShareDel
diff --git a/src/internal/syscall/windows/zsyscall_windows.go b/src/internal/syscall/windows/zsyscall_windows.go
index f6a8954072..55af05d3e9 100644
--- a/src/internal/syscall/windows/zsyscall_windows.go
+++ b/src/internal/syscall/windows/zsyscall_windows.go
@@ -38,6 +38,7 @@ func errnoErr(e syscall.Errno) error {
 var (
 	modiphlpapi = syscall.NewLazyDLL(sysdll.Add("iphlpapi.dll"))
 	modkernel32 = syscall.NewLazyDLL(sysdll.Add("kernel32.dll"))
+	modnetapi32 = syscall.NewLazyDLL(sysdll.Add("netapi32.dll"))
 	modadvapi32 = syscall.NewLazyDLL(sysdll.Add("advapi32.dll"))
 
 	procGetAdaptersAddresses  = modiphlpapi.NewProc("GetAdaptersAddresses")
@@ -47,6 +48,8 @@ var (
 	procGetConsoleCP          = modkernel32.NewProc("GetConsoleCP")
 	procMultiByteToWideChar   = modkernel32.NewProc("MultiByteToWideChar")
 	procGetCurrentThread      = modkernel32.NewProc("GetCurrentThread")
+	procNetShareAdd           = modnetapi32.NewProc("NetShareAdd")
+	procNetShareDel           = modnetapi32.NewProc("NetShareDel")
 	procImpersonateSelf       = modadvapi32.NewProc("ImpersonateSelf")
 	procRevertToSelf          = modadvapi32.NewProc("RevertToSelf")
 	procOpenThreadToken       = modadvapi32.NewProc("OpenThreadToken")
@@ -124,6 +127,22 @@ func GetCurrentThread() (pseudoHandle syscall.Handle, err error) {
 	return
 }
 
+func NetShareAdd(serverName *uint16, level uint32, buf *byte, parmErr *uint16) (neterr error) {
+	r0, _, _ := syscall.Syscall6(procNetShareAdd.Addr(), 4, uintptr(unsafe.Pointer(serverName)), uintptr(level), uintptr(unsafe.Pointer(buf)), uintptr(unsafe.Pointer(parmErr)), 0, 0)
+	if r0 != 0 {
+		neterr = syscall.Errno(r0)
+	}
+	return
+}
+
+func NetShareDel(serverName *uint16, netName *uint16, reserved uint32) (neterr error) {
+	r0, _, _ := syscall.Syscall(procNetShareDel.Addr(), 3, uintptr(unsafe.Pointer(serverName)), uintptr(unsafe.Pointer(netName)), uintptr(reserved))
+	if r0 != 0 {
+		neterr = syscall.Errno(r0)
+	}
+	return
+}
+
 func ImpersonateSelf(impersonationlevel uint32) (err error) {
 	r1, _, e1 := syscall.Syscall(procImpersonateSelf.Addr(), 1, uintptr(impersonationlevel), 0, 0)
 	if r1 == 0 {
diff --git a/src/os/os_windows_test.go b/src/os/os_windows_test.go
index 1a7946ae9f..72af075e5b 100644
--- a/src/os/os_windows_test.go
+++ b/src/os/os_windows_test.go
@@ -263,7 +263,6 @@ func TestDirectoryJunction(t *testing.T) {
 				t.addPrintName("")
 				return createMountPoint(link, &t)
 			},
-			issueNo: 16145,
 		},
 	}
 	output, _ := osexec.Command("cmd", "/c", "mklink", "/?").Output()
@@ -396,12 +395,106 @@ func TestDirectorySymbolicLink(t *testing.T) {
 				t.addPrintNameNoNUL(filepath.Base(target))
 				return createSymbolicLink(link, &t, true)
 			},
-			issueNo: 15978,
 		},
 	)
 	testDirLinks(t, tests)
 }
 
+func TestNetworkSymbolicLink(t *testing.T) {
+	testenv.MustHaveSymlink(t)
+
+	dir, err := ioutil.TempDir("", "TestNetworkSymbolicLink")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	oldwd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = os.Chdir(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Chdir(oldwd)
+
+	shareName := "GoSymbolicLinkTestShare" // hope no conflictions
+	sharePath := filepath.Join(dir, shareName)
+	testDir := "TestDir"
+
+	err = os.MkdirAll(filepath.Join(sharePath, testDir), 0777)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	wShareName, err := syscall.UTF16PtrFromString(shareName)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wSharePath, err := syscall.UTF16PtrFromString(sharePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	p := windows.SHARE_INFO_2{
+		Netname:     wShareName,
+		Type:        windows.STYPE_DISKTREE,
+		Remark:      nil,
+		Permissions: 0,
+		MaxUses:     1,
+		CurrentUses: 0,
+		Path:        wSharePath,
+		Passwd:      nil,
+	}
+
+	err = windows.NetShareAdd(nil, 2, (*byte)(unsafe.Pointer(&p)), nil)
+	if err != nil {
+		if err == syscall.ERROR_ACCESS_DENIED {
+			t.Skip("you don't have enough privileges to add network share")
+		}
+		t.Fatal(err)
+	}
+	defer func() {
+		err := windows.NetShareDel(nil, wShareName, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	UNCPath := `\\localhost\` + shareName + `\`
+
+	fi1, err := os.Stat(sharePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	fi2, err := os.Stat(UNCPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !os.SameFile(fi1, fi2) {
+		t.Fatalf("%q and %q should be the same directory, but not", sharePath, UNCPath)
+	}
+
+	target := filepath.Join(UNCPath, testDir)
+	link := "link"
+
+	err = os.Symlink(target, link)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(link)
+
+	got, err := os.Readlink(link)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if got != target {
+		t.Errorf(`os.Readlink("%s"): got %v, want %v`, link, got, target)
+	}
+}
+
 func TestStartProcessAttr(t *testing.T) {
 	p, err := os.StartProcess(os.Getenv("COMSPEC"), []string{"/c", "cd"}, new(os.ProcAttr))
 	if err != nil {
diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go
index e13d6e2dd5..f4f8f3ad09 100644
--- a/src/syscall/syscall_windows.go
+++ b/src/syscall/syscall_windows.go
@@ -1024,11 +1024,31 @@ func Readlink(path string, buf []byte) (n int, err error) {
 	case IO_REPARSE_TAG_SYMLINK:
 		data := (*symbolicLinkReparseBuffer)(unsafe.Pointer(&rdb.reparseBuffer))
 		p := (*[0xffff]uint16)(unsafe.Pointer(&data.PathBuffer[0]))
-		s = UTF16ToString(p[data.PrintNameOffset/2 : (data.PrintNameLength-data.PrintNameOffset)/2])
+		s = UTF16ToString(p[data.SubstituteNameOffset/2 : (data.SubstituteNameOffset+data.SubstituteNameLength)/2])
+		if data.Flags&_SYMLINK_FLAG_RELATIVE == 0 {
+			if len(s) >= 4 && s[:4] == `\??\` {
+				s = s[4:]
+				switch {
+				case len(s) >= 2 && s[1] == ':': // \??\C:\foo\bar
+					// do nothing
+				case len(s) >= 4 && s[:4] == `UNC\`: // \??\UNC\foo\bar
+					s = `\\` + s[4:]
+				default:
+					// unexpected; do nothing
+				}
+			} else {
+				// unexpected; do nothing
+			}
+		}
 	case _IO_REPARSE_TAG_MOUNT_POINT:
 		data := (*mountPointReparseBuffer)(unsafe.Pointer(&rdb.reparseBuffer))
 		p := (*[0xffff]uint16)(unsafe.Pointer(&data.PathBuffer[0]))
-		s = UTF16ToString(p[data.PrintNameOffset/2 : (data.PrintNameLength-data.PrintNameOffset)/2])
+		s = UTF16ToString(p[data.SubstituteNameOffset/2 : (data.SubstituteNameOffset+data.SubstituteNameLength)/2])
+		if len(s) >= 4 && s[:4] == `\??\` { // \??\C:\foo\bar
+			s = s[4:]
+		} else {
+			// unexpected; do nothing
+		}
 	default:
 		// the path is not a symlink or junction but another type of reparse
 		// point
diff --git a/src/syscall/ztypes_windows.go b/src/syscall/ztypes_windows.go
index 8c2e19653a..1fb6f5c29f 100644
--- a/src/syscall/ztypes_windows.go
+++ b/src/syscall/ztypes_windows.go
@@ -1116,4 +1116,5 @@ const (
 	_IO_REPARSE_TAG_MOUNT_POINT      = 0xA0000003
 	IO_REPARSE_TAG_SYMLINK           = 0xA000000C
 	SYMBOLIC_LINK_FLAG_DIRECTORY     = 0x1
+	_SYMLINK_FLAG_RELATIVE           = 1
 )