syscall: preserve Windows file permissions for O_CREAT|O_TRUNC
On Windows, calling syscall.Open(file, O_CREAT|O_TRUNC, 0) for a file
that already exists would change the file to be read-only.
That is not how the Unix syscall.Open behaves, so avoid it on
Windows by calling CreateFile twice if necessary.
Fixes #38225
Change-Id: I70097fca8863df427cc8a97b9376a9ffc69c6318
Reviewed-on: https://go-review.googlesource.com/c/go/+/234534
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
diff --git a/src/os/os_test.go b/src/os/os_test.go
index f86428b..e8c6451 100644
--- a/src/os/os_test.go
+++ b/src/os/os_test.go
@@ -2539,3 +2539,34 @@
}
return true
}
+
+// Test that opening a file does not change its permissions. Issue 38225.
+func TestOpenFileKeepsPermissions(t *testing.T) {
+ t.Parallel()
+ dir := t.TempDir()
+ name := filepath.Join(dir, "x")
+ f, err := Create(name)
+ if err != nil {
+ t.Fatal(err)
+ }
+ if err := f.Close(); err != nil {
+ t.Error(err)
+ }
+ f, err = OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, 0)
+ if err != nil {
+ t.Fatal(err)
+ }
+ if fi, err := f.Stat(); err != nil {
+ t.Error(err)
+ } else if fi.Mode()&0222 == 0 {
+ t.Errorf("f.Stat.Mode after OpenFile is %v, should be writable", fi.Mode())
+ }
+ if err := f.Close(); err != nil {
+ t.Error(err)
+ }
+ if fi, err := Stat(name); err != nil {
+ t.Error(err)
+ } else if fi.Mode()&0222 == 0 {
+ t.Errorf("Stat after OpenFile is %v, should be writable", fi.Mode())
+ }
+}
diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go
index 89c0a93..f62c00d 100644
--- a/src/syscall/syscall_windows.go
+++ b/src/syscall/syscall_windows.go
@@ -339,6 +339,26 @@
var attrs uint32 = FILE_ATTRIBUTE_NORMAL
if perm&S_IWRITE == 0 {
attrs = FILE_ATTRIBUTE_READONLY
+ if createmode == CREATE_ALWAYS {
+ // We have been asked to create a read-only file.
+ // If the file already exists, the semantics of
+ // the Unix open system call is to preserve the
+ // existing permissions. If we pass CREATE_ALWAYS
+ // and FILE_ATTRIBUTE_READONLY to CreateFile,
+ // and the file already exists, CreateFile will
+ // change the file permissions.
+ // Avoid that to preserve the Unix semantics.
+ h, e := CreateFile(pathp, access, sharemode, sa, TRUNCATE_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)
+ switch e {
+ case ERROR_FILE_NOT_FOUND, _ERROR_BAD_NETPATH, ERROR_PATH_NOT_FOUND:
+ // File does not exist. These are the same
+ // errors as Errno.Is checks for ErrNotExist.
+ // Carry on to create the file.
+ default:
+ // Success or some different error.
+ return h, e
+ }
+ }
}
h, e := CreateFile(pathp, access, sharemode, sa, createmode, attrs, 0)
return h, e
