os: make MkdirAll support volume names

MkdirAll fails to create directories under root paths using volume
names (e.g. //?/Volume{GUID}/foo). This is because fixRootDirectory
only handle extended length paths using drive letters (e.g. //?/C:/foo).

This CL fixes that issue by also detecting volume names without path
separator.

Updates #22230
Fixes #39785

Change-Id: I813fdc0b968ce71a4297f69245b935558e6cd789
Reviewed-on: https://go-review.googlesource.com/c/go/+/517015
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

7 files changed, 118 insertions, 64 deletions

diff --git a/src/internal/syscall/windows/syscall_windows.go b/src/internal/syscall/windows/syscall_windows.go
index 924dd1e121..ad36bd48a6 100644
--- a/src/internal/syscall/windows/syscall_windows.go
+++ b/src/internal/syscall/windows/syscall_windows.go
@@ -398,6 +398,7 @@ type FILE_ID_BOTH_DIR_INFO struct {
 }
 
 //sys	GetVolumeInformationByHandle(file syscall.Handle, volumeNameBuffer *uint16, volumeNameSize uint32, volumeNameSerialNumber *uint32, maximumComponentLength *uint32, fileSystemFlags *uint32, fileSystemNameBuffer *uint16, fileSystemNameSize uint32) (err error) = GetVolumeInformationByHandleW
+//sys	GetVolumeNameForVolumeMountPoint(volumeMountPoint *uint16, volumeName *uint16, bufferlength uint32) (err error) = GetVolumeNameForVolumeMountPointW
 
 //sys	RtlLookupFunctionEntry(pc uintptr, baseAddress *uintptr, table *byte) (ret uintptr) = kernel32.RtlLookupFunctionEntry
 //sys	RtlVirtualUnwind(handlerType uint32, baseAddress uintptr, pc uintptr, entry uintptr, ctxt uintptr, data *uintptr, frame *uintptr, ctxptrs *byte) (ret uintptr) = kernel32.RtlVirtualUnwind
diff --git a/src/internal/syscall/windows/zsyscall_windows.go b/src/internal/syscall/windows/zsyscall_windows.go
index fb87bd03a2..e3f6d8d2a2 100644
--- a/src/internal/syscall/windows/zsyscall_windows.go
+++ b/src/internal/syscall/windows/zsyscall_windows.go
@@ -45,46 +45,47 @@ var (
 	moduserenv  = syscall.NewLazyDLL(sysdll.Add("userenv.dll"))
 	modws2_32   = syscall.NewLazyDLL(sysdll.Add("ws2_32.dll"))
 
-	procAdjustTokenPrivileges         = modadvapi32.NewProc("AdjustTokenPrivileges")
-	procDuplicateTokenEx              = modadvapi32.NewProc("DuplicateTokenEx")
-	procImpersonateSelf               = modadvapi32.NewProc("ImpersonateSelf")
-	procLookupPrivilegeValueW         = modadvapi32.NewProc("LookupPrivilegeValueW")
-	procOpenSCManagerW                = modadvapi32.NewProc("OpenSCManagerW")
-	procOpenServiceW                  = modadvapi32.NewProc("OpenServiceW")
-	procOpenThreadToken               = modadvapi32.NewProc("OpenThreadToken")
-	procQueryServiceStatus            = modadvapi32.NewProc("QueryServiceStatus")
-	procRevertToSelf                  = modadvapi32.NewProc("RevertToSelf")
-	procSetTokenInformation           = modadvapi32.NewProc("SetTokenInformation")
-	procSystemFunction036             = modadvapi32.NewProc("SystemFunction036")
-	procGetAdaptersAddresses          = modiphlpapi.NewProc("GetAdaptersAddresses")
-	procCreateEventW                  = modkernel32.NewProc("CreateEventW")
-	procGetACP                        = modkernel32.NewProc("GetACP")
-	procGetComputerNameExW            = modkernel32.NewProc("GetComputerNameExW")
-	procGetConsoleCP                  = modkernel32.NewProc("GetConsoleCP")
-	procGetCurrentThread              = modkernel32.NewProc("GetCurrentThread")
-	procGetFileInformationByHandleEx  = modkernel32.NewProc("GetFileInformationByHandleEx")
-	procGetFinalPathNameByHandleW     = modkernel32.NewProc("GetFinalPathNameByHandleW")
-	procGetModuleFileNameW            = modkernel32.NewProc("GetModuleFileNameW")
-	procGetTempPath2W                 = modkernel32.NewProc("GetTempPath2W")
-	procGetVolumeInformationByHandleW = modkernel32.NewProc("GetVolumeInformationByHandleW")
-	procLockFileEx                    = modkernel32.NewProc("LockFileEx")
-	procModule32FirstW                = modkernel32.NewProc("Module32FirstW")
-	procModule32NextW                 = modkernel32.NewProc("Module32NextW")
-	procMoveFileExW                   = modkernel32.NewProc("MoveFileExW")
-	procMultiByteToWideChar           = modkernel32.NewProc("MultiByteToWideChar")
-	procRtlLookupFunctionEntry        = modkernel32.NewProc("RtlLookupFunctionEntry")
-	procRtlVirtualUnwind              = modkernel32.NewProc("RtlVirtualUnwind")
-	procSetFileInformationByHandle    = modkernel32.NewProc("SetFileInformationByHandle")
-	procUnlockFileEx                  = modkernel32.NewProc("UnlockFileEx")
-	procVirtualQuery                  = modkernel32.NewProc("VirtualQuery")
-	procNetShareAdd                   = modnetapi32.NewProc("NetShareAdd")
-	procNetShareDel                   = modnetapi32.NewProc("NetShareDel")
-	procNetUserGetLocalGroups         = modnetapi32.NewProc("NetUserGetLocalGroups")
-	procGetProcessMemoryInfo          = modpsapi.NewProc("GetProcessMemoryInfo")
-	procCreateEnvironmentBlock        = moduserenv.NewProc("CreateEnvironmentBlock")
-	procDestroyEnvironmentBlock       = moduserenv.NewProc("DestroyEnvironmentBlock")
-	procGetProfilesDirectoryW         = moduserenv.NewProc("GetProfilesDirectoryW")
-	procWSASocketW                    = modws2_32.NewProc("WSASocketW")
+	procAdjustTokenPrivileges             = modadvapi32.NewProc("AdjustTokenPrivileges")
+	procDuplicateTokenEx                  = modadvapi32.NewProc("DuplicateTokenEx")
+	procImpersonateSelf                   = modadvapi32.NewProc("ImpersonateSelf")
+	procLookupPrivilegeValueW             = modadvapi32.NewProc("LookupPrivilegeValueW")
+	procOpenSCManagerW                    = modadvapi32.NewProc("OpenSCManagerW")
+	procOpenServiceW                      = modadvapi32.NewProc("OpenServiceW")
+	procOpenThreadToken                   = modadvapi32.NewProc("OpenThreadToken")
+	procQueryServiceStatus                = modadvapi32.NewProc("QueryServiceStatus")
+	procRevertToSelf                      = modadvapi32.NewProc("RevertToSelf")
+	procSetTokenInformation               = modadvapi32.NewProc("SetTokenInformation")
+	procSystemFunction036                 = modadvapi32.NewProc("SystemFunction036")
+	procGetAdaptersAddresses              = modiphlpapi.NewProc("GetAdaptersAddresses")
+	procCreateEventW                      = modkernel32.NewProc("CreateEventW")
+	procGetACP                            = modkernel32.NewProc("GetACP")
+	procGetComputerNameExW                = modkernel32.NewProc("GetComputerNameExW")
+	procGetConsoleCP                      = modkernel32.NewProc("GetConsoleCP")
+	procGetCurrentThread                  = modkernel32.NewProc("GetCurrentThread")
+	procGetFileInformationByHandleEx      = modkernel32.NewProc("GetFileInformationByHandleEx")
+	procGetFinalPathNameByHandleW         = modkernel32.NewProc("GetFinalPathNameByHandleW")
+	procGetModuleFileNameW                = modkernel32.NewProc("GetModuleFileNameW")
+	procGetTempPath2W                     = modkernel32.NewProc("GetTempPath2W")
+	procGetVolumeInformationByHandleW     = modkernel32.NewProc("GetVolumeInformationByHandleW")
+	procGetVolumeNameForVolumeMountPointW = modkernel32.NewProc("GetVolumeNameForVolumeMountPointW")
+	procLockFileEx                        = modkernel32.NewProc("LockFileEx")
+	procModule32FirstW                    = modkernel32.NewProc("Module32FirstW")
+	procModule32NextW                     = modkernel32.NewProc("Module32NextW")
+	procMoveFileExW                       = modkernel32.NewProc("MoveFileExW")
+	procMultiByteToWideChar               = modkernel32.NewProc("MultiByteToWideChar")
+	procRtlLookupFunctionEntry            = modkernel32.NewProc("RtlLookupFunctionEntry")
+	procRtlVirtualUnwind                  = modkernel32.NewProc("RtlVirtualUnwind")
+	procSetFileInformationByHandle        = modkernel32.NewProc("SetFileInformationByHandle")
+	procUnlockFileEx                      = modkernel32.NewProc("UnlockFileEx")
+	procVirtualQuery                      = modkernel32.NewProc("VirtualQuery")
+	procNetShareAdd                       = modnetapi32.NewProc("NetShareAdd")
+	procNetShareDel                       = modnetapi32.NewProc("NetShareDel")
+	procNetUserGetLocalGroups             = modnetapi32.NewProc("NetUserGetLocalGroups")
+	procGetProcessMemoryInfo              = modpsapi.NewProc("GetProcessMemoryInfo")
+	procCreateEnvironmentBlock            = moduserenv.NewProc("CreateEnvironmentBlock")
+	procDestroyEnvironmentBlock           = moduserenv.NewProc("DestroyEnvironmentBlock")
+	procGetProfilesDirectoryW             = moduserenv.NewProc("GetProfilesDirectoryW")
+	procWSASocketW                        = modws2_32.NewProc("WSASocketW")
 )
 
 func adjustTokenPrivileges(token syscall.Token, disableAllPrivileges bool, newstate *TOKEN_PRIVILEGES, buflen uint32, prevstate *TOKEN_PRIVILEGES, returnlen *uint32) (ret uint32, err error) {
@@ -279,6 +280,14 @@ func GetVolumeInformationByHandle(file syscall.Handle, volumeNameBuffer *uint16,
 	return
 }
 
+func GetVolumeNameForVolumeMountPoint(volumeMountPoint *uint16, volumeName *uint16, bufferlength uint32) (err error) {
+	r1, _, e1 := syscall.Syscall(procGetVolumeNameForVolumeMountPointW.Addr(), 3, uintptr(unsafe.Pointer(volumeMountPoint)), uintptr(unsafe.Pointer(volumeName)), uintptr(bufferlength))
+	if r1 == 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
 func LockFileEx(file syscall.Handle, flags uint32, reserved uint32, bytesLow uint32, bytesHigh uint32, overlapped *syscall.Overlapped) (err error) {
 	r1, _, e1 := syscall.Syscall6(procLockFileEx.Addr(), 6, uintptr(file), uintptr(flags), uintptr(reserved), uintptr(bytesLow), uintptr(bytesHigh), uintptr(unsafe.Pointer(overlapped)))
 	if r1 == 0 {
diff --git a/src/os/path.go b/src/os/path.go
index df87887b9b..6ac4cbe20f 100644
--- a/src/os/path.go
+++ b/src/os/path.go
@@ -26,19 +26,25 @@ func MkdirAll(path string, perm FileMode) error {
 	}
 
 	// Slow path: make sure parent exists and then call Mkdir for path.
-	i := len(path)
-	for i > 0 && IsPathSeparator(path[i-1]) { // Skip trailing path separator.
+
+	// Extract the parent folder from path by first removing any trailing
+	// path separator and then scanning backward until finding a path
+	// separator or reaching the beginning of the string.
+	i := len(path) - 1
+	for i >= 0 && IsPathSeparator(path[i]) {
 		i--
 	}
-
-	j := i
-	for j > 0 && !IsPathSeparator(path[j-1]) { // Scan backward over element.
-		j--
+	for i >= 0 && !IsPathSeparator(path[i]) {
+		i--
+	}
+	if i < 0 {
+		i = 0
 	}
 
-	if j > 1 {
-		// Create parent.
-		err = MkdirAll(fixRootDirectory(path[:j-1]), perm)
+	// If there is a parent directory, and it is not the volume name,
+	// recurse to ensure parent directory exists.
+	if parent := path[:i]; len(parent) > len(volumeName(path)) {
+		err = MkdirAll(parent, perm)
 		if err != nil {
 			return err
 		}
diff --git a/src/os/path_plan9.go b/src/os/path_plan9.go
index a54b4b98f1..f1c9dbc048 100644
--- a/src/os/path_plan9.go
+++ b/src/os/path_plan9.go
@@ -14,6 +14,6 @@ func IsPathSeparator(c uint8) bool {
 	return PathSeparator == c
 }
 
-func fixRootDirectory(p string) string {
-	return p
+func volumeName(p string) string {
+	return ""
 }
diff --git a/src/os/path_unix.go b/src/os/path_unix.go
index c975cdb11e..1c80fa91f8 100644
--- a/src/os/path_unix.go
+++ b/src/os/path_unix.go
@@ -70,6 +70,6 @@ func splitPath(path string) (string, string) {
 	return dirname, basename
 }
 
-func fixRootDirectory(p string) string {
-	return p
+func volumeName(p string) string {
+	return ""
 }
diff --git a/src/os/path_windows.go b/src/os/path_windows.go
index 3356908a36..ec9a87274d 100644
--- a/src/os/path_windows.go
+++ b/src/os/path_windows.go
@@ -214,14 +214,3 @@ func fixLongPath(path string) string {
 	}
 	return string(pathbuf[:w])
 }
-
-// fixRootDirectory fixes a reference to a drive's root directory to
-// have the required trailing slash.
-func fixRootDirectory(p string) string {
-	if len(p) == len(`\\?\c:`) {
-		if IsPathSeparator(p[0]) && IsPathSeparator(p[1]) && p[2] == '?' && IsPathSeparator(p[3]) && p[5] == ':' {
-			return p + `\`
-		}
-	}
-	return p
-}
diff --git a/src/os/path_windows_test.go b/src/os/path_windows_test.go
index 2506b4f0d8..4e5e501d1f 100644
--- a/src/os/path_windows_test.go
+++ b/src/os/path_windows_test.go
@@ -5,7 +5,11 @@
 package os_test
 
 import (
+	"fmt"
+	"internal/syscall/windows"
+	"internal/testenv"
 	"os"
+	"path/filepath"
 	"strings"
 	"syscall"
 	"testing"
@@ -106,3 +110,48 @@ func TestOpenRootSlash(t *testing.T) {
 		dir.Close()
 	}
 }
+
+func testMkdirAllAtRoot(t *testing.T, root string) {
+	// Create a unique-enough directory name in root.
+	base := fmt.Sprintf("%s-%d", t.Name(), os.Getpid())
+	path := filepath.Join(root, base)
+	if err := os.MkdirAll(path, 0777); err != nil {
+		t.Fatalf("MkdirAll(%q) failed: %v", path, err)
+	}
+	// Clean up
+	if err := os.RemoveAll(path); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestMkdirAllExtendedLengthAtRoot(t *testing.T) {
+	if testenv.Builder() == "" {
+		t.Skipf("skipping non-hermetic test outside of Go builders")
+	}
+
+	const prefix = `\\?\`
+	vol := filepath.VolumeName(t.TempDir()) + `\`
+	if len(vol) < 4 || vol[:4] != prefix {
+		vol = prefix + vol
+	}
+	testMkdirAllAtRoot(t, vol)
+}
+
+func TestMkdirAllVolumeNameAtRoot(t *testing.T) {
+	if testenv.Builder() == "" {
+		t.Skipf("skipping non-hermetic test outside of Go builders")
+	}
+
+	vol, err := syscall.UTF16PtrFromString(filepath.VolumeName(t.TempDir()) + `\`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	const maxVolNameLen = 50
+	var buf [maxVolNameLen]uint16
+	err = windows.GetVolumeNameForVolumeMountPoint(vol, &buf[0], maxVolNameLen)
+	if err != nil {
+		t.Fatal(err)
+	}
+	volName := syscall.UTF16ToString(buf[:])
+	testMkdirAllAtRoot(t, volName)
+}