windows: fix race when allocating buffer for some windows syscalls

From main repo: https://go-review.googlesource.com/#/c/4940

Change-Id: I56fe7f6aedc0fd350abb94299ad500fcb80c049a
Reviewed-on: https://go-review.googlesource.com/8604
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

windows/env_windows.go

@@ -16,19 +16,17 @@ func Getenv(key string) (value string, found bool) {
 	if err != nil {
 		return "", false
 	}
-	b := make([]uint16, 100)
-	n, e := GetEnvironmentVariable(keyp, &b[0], uint32(len(b)))
-	if n == 0 && e == ERROR_ENVVAR_NOT_FOUND {
-		return "", false
-	}
-	if n > uint32(len(b)) {
-		b = make([]uint16, n)
-		n, e = GetEnvironmentVariable(keyp, &b[0], uint32(len(b)))
-		if n > uint32(len(b)) {
-			n = 0
+	n := uint32(100)
+	for {
+		b := make([]uint16, n)
+		n, err = GetEnvironmentVariable(keyp, &b[0], uint32(len(b)))
+		if n == 0 && err == ERROR_ENVVAR_NOT_FOUND {
+			return "", false
+		}
+		if n <= uint32(len(b)) {
+			return string(utf16.Decode(b[:n])), true
 		}
 	}
-	return string(utf16.Decode(b[0:n])), true
 }
 
 func Setenv(key, value string) error {

windows/exec_windows.go

@@ -6,8 +6,6 @@
 
 package windows
 
-import "syscall"
-
 // EscapeArg rewrites command line argument s as prescribed
 // in http://msdn.microsoft.com/en-us/library/ms880421.
 // This function returns "" (2 double quotes) if s is empty.
@@ -85,21 +83,15 @@ func FullPath(name string) (path string, err error) {
 	if err != nil {
 		return "", err
 	}
-	buf := make([]uint16, 100)
-	n, err := GetFullPathName(p, uint32(len(buf)), &buf[0], nil)
-	if err != nil {
-		return "", err
-	}
-	if n > uint32(len(buf)) {
-		// Windows is asking for bigger buffer.
-		buf = make([]uint16, n)
+	n := uint32(100)
+	for {
+		buf := make([]uint16, n)
 		n, err = GetFullPathName(p, uint32(len(buf)), &buf[0], nil)
 		if err != nil {
 			return "", err
 		}
-		if n > uint32(len(buf)) {
-			return "", syscall.EINVAL
+		if n <= uint32(len(buf)) {
+			return UTF16ToString(buf[:n]), nil
 		}
 	}
-	return UTF16ToString(buf[:n]), nil
 }

windows/security_windows.go

@@ -42,21 +42,20 @@ func TranslateAccountName(username string, from, to uint32, initSize int) (strin
 	if e != nil {
 		return "", e
 	}
-	b := make([]uint16, 50)
-	n := uint32(len(b))
-	e = TranslateName(u, from, to, &b[0], &n)
-	if e != nil {
+	n := uint32(50)
+	for {
+		b := make([]uint16, n)
+		e = TranslateName(u, from, to, &b[0], &n)
+		if e == nil {
+			return UTF16ToString(b[:n]), nil
+		}
 		if e != ERROR_INSUFFICIENT_BUFFER {
 			return "", e
 		}
-		// make receive buffers of requested size and try again
-		b = make([]uint16, n)
-		e = TranslateName(u, from, to, &b[0], &n)
-		if e != nil {
+		if n <= uint32(len(b)) {
 			return "", e
 		}
 	}
-	return UTF16ToString(b), nil
 }
 
 const (
@@ -137,26 +136,23 @@ func LookupSID(system, account string) (sid *SID, domain string, accType uint32,
 			return nil, "", 0, e
 		}
 	}
-	db := make([]uint16, 50)
-	dn := uint32(len(db))
-	b := make([]byte, 50)
-	n := uint32(len(b))
-	sid = (*SID)(unsafe.Pointer(&b[0]))
-	e = LookupAccountName(sys, acc, sid, &n, &db[0], &dn, &accType)
-	if e != nil {
+	n := uint32(50)
+	dn := uint32(50)
+	for {
+		b := make([]byte, n)
+		db := make([]uint16, dn)
+		sid = (*SID)(unsafe.Pointer(&b[0]))
+		e = LookupAccountName(sys, acc, sid, &n, &db[0], &dn, &accType)
+		if e == nil {
+			return sid, UTF16ToString(db), accType, nil
+		}
 		if e != ERROR_INSUFFICIENT_BUFFER {
 			return nil, "", 0, e
 		}
-		// make receive buffers of requested size and try again
-		b = make([]byte, n)
-		sid = (*SID)(unsafe.Pointer(&b[0]))
-		db = make([]uint16, dn)
-		e = LookupAccountName(sys, acc, sid, &n, &db[0], &dn, &accType)
-		if e != nil {
+		if n <= uint32(len(b)) {
 			return nil, "", 0, e
 		}
 	}
-	return sid, UTF16ToString(db), accType, nil
 }
 
 // String converts sid to a string format
@@ -198,24 +194,22 @@ func (sid *SID) LookupAccount(system string) (account, domain string, accType ui
 			return "", "", 0, err
 		}
 	}
-	b := make([]uint16, 50)
-	n := uint32(len(b))
-	db := make([]uint16, 50)
-	dn := uint32(len(db))
-	e := LookupAccountSid(sys, sid, &b[0], &n, &db[0], &dn, &accType)
-	if e != nil {
+	n := uint32(50)
+	dn := uint32(50)
+	for {
+		b := make([]uint16, n)
+		db := make([]uint16, dn)
+		e := LookupAccountSid(sys, sid, &b[0], &n, &db[0], &dn, &accType)
+		if e == nil {
+			return UTF16ToString(b), UTF16ToString(db), accType, nil
+		}
 		if e != ERROR_INSUFFICIENT_BUFFER {
 			return "", "", 0, e
 		}
-		// make receive buffers of requested size and try again
-		b = make([]uint16, n)
-		db = make([]uint16, dn)
-		e = LookupAccountSid(nil, sid, &b[0], &n, &db[0], &dn, &accType)
-		if e != nil {
+		if n <= uint32(len(b)) {
 			return "", "", 0, e
 		}
 	}
-	return UTF16ToString(b), UTF16ToString(db), accType, nil
 }
 
 const (
@@ -327,21 +321,20 @@ func (t Token) Close() error {
 
 // getInfo retrieves a specified type of information about an access token.
 func (t Token) getInfo(class uint32, initSize int) (unsafe.Pointer, error) {
-	b := make([]byte, initSize)
-	var n uint32
-	e := GetTokenInformation(t, class, &b[0], uint32(len(b)), &n)
-	if e != nil {
+	n := uint32(initSize)
+	for {
+		b := make([]byte, n)
+		e := GetTokenInformation(t, class, &b[0], uint32(len(b)), &n)
+		if e == nil {
+			return unsafe.Pointer(&b[0]), nil
+		}
 		if e != ERROR_INSUFFICIENT_BUFFER {
 			return nil, e
 		}
-		// make receive buffers of requested size and try again
-		b = make([]byte, n)
-		e = GetTokenInformation(t, class, &b[0], uint32(len(b)), &n)
-		if e != nil {
+		if n <= uint32(len(b)) {
 			return nil, e
 		}
 	}
-	return unsafe.Pointer(&b[0]), nil
 }
 
 // GetTokenUser retrieves access token t user account information.
@@ -367,19 +360,18 @@ func (t Token) GetTokenPrimaryGroup() (*Tokenprimarygroup, error) {
 // GetUserProfileDirectory retrieves path to the
 // root directory of the access token t user's profile.
 func (t Token) GetUserProfileDirectory() (string, error) {
-	b := make([]uint16, 100)
-	n := uint32(len(b))
-	e := GetUserProfileDirectory(t, &b[0], &n)
-	if e != nil {
+	n := uint32(100)
+	for {
+		b := make([]uint16, n)
+		e := GetUserProfileDirectory(t, &b[0], &n)
+		if e == nil {
+			return UTF16ToString(b), nil
+		}
 		if e != ERROR_INSUFFICIENT_BUFFER {
 			return "", e
 		}
-		// make receive buffers of requested size and try again
-		b = make([]uint16, n)
-		e = GetUserProfileDirectory(t, &b[0], &n)
-		if e != nil {
+		if n <= uint32(len(b)) {
 			return "", e
 		}
 	}
-	return UTF16ToString(b), nil
 }