internal/syscall/windows: set write access when O_TRUNC is used

Whenn O_TRUNC is set, Opentat ends up calling syscall.Ftruncate, which
needs write access. Make sure write access is not removed when O_TRUNC
and O_APPEND are both set.

Updates #67002.

Change-Id: Iccc470b7be3c62144318d6a707057504f3b74c97
Reviewed-on: https://go-review.googlesource.com/c/go/+/620576
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

diff --git a/src/internal/syscall/windows/at_windows.go b/src/internal/syscall/windows/at_windows.go
index 064564c5e08334000d1b9ae767a49710cf6011b5..ad4a0ab25bbf4e6677fab9d4ad5c782493ed14b0 100644 (file)
--- a/src/internal/syscall/windows/at_windows.go
+++ b/src/internal/syscall/windows/at_windows.go
@@ -41,8 +41,12 @@ func Openat(dirfd syscall.Handle, name string, flag int, perm uint32) (_ syscall
                access |= FILE_GENERIC_WRITE
        }
        if flag&syscall.O_APPEND != 0 {
-               access &^= FILE_WRITE_DATA
                access |= FILE_APPEND_DATA
+               // Remove GENERIC_WRITE access unless O_TRUNC is set,
+               // in which case we need it to truncate the file.
+               if flag&syscall.O_TRUNC == 0 {
+                       access &^= FILE_WRITE_DATA
+               }
        }
        if flag&O_DIRECTORY != 0 {
                options |= FILE_DIRECTORY_FILE

diff --git a/src/internal/syscall/windows/at_windows_test.go b/src/internal/syscall/windows/at_windows_test.go
new file mode 100644 (file)
index 0000000..7da9ecf
--- /dev/null
+++ b/src/internal/syscall/windows/at_windows_test.go
@@ -0,0 +1,58 @@
+// Copyright 2024 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.
+
+package windows_test
+
+import (
+       "internal/syscall/windows"
+       "os"
+       "path/filepath"
+       "syscall"
+       "testing"
+)
+
+func TestOpen(t *testing.T) {
+       t.Parallel()
+
+       dir := t.TempDir()
+       file := filepath.Join(dir, "a")
+       f, err := os.Create(file)
+       if err != nil {
+               t.Fatal(err)
+       }
+       f.Close()
+
+       tests := []struct {
+               path string
+               flag int
+               err  error
+       }{
+               {dir, syscall.O_RDONLY, nil},
+               {dir, syscall.O_CREAT, nil},
+               {dir, syscall.O_RDONLY | syscall.O_CREAT, nil},
+               {file, syscall.O_APPEND | syscall.O_WRONLY | os.O_CREATE, nil},
+               {file, syscall.O_APPEND | syscall.O_WRONLY | os.O_CREATE | os.O_TRUNC, nil},
+               {dir, syscall.O_RDONLY | syscall.O_TRUNC, syscall.ERROR_ACCESS_DENIED},
+               {dir, syscall.O_WRONLY | syscall.O_RDWR, nil}, // TODO: syscall.Open returns EISDIR here, we should reconcile this
+               {dir, syscall.O_WRONLY, syscall.EISDIR},
+               {dir, syscall.O_RDWR, syscall.EISDIR},
+       }
+       for i, tt := range tests {
+               dir := filepath.Dir(tt.path)
+               dirfd, err := syscall.Open(dir, syscall.O_RDONLY, 0)
+               if err != nil {
+                       t.Error(err)
+                       continue
+               }
+               base := filepath.Base(tt.path)
+               h, err := windows.Openat(dirfd, base, tt.flag, 0o660)
+               syscall.CloseHandle(dirfd)
+               if err == nil {
+                       syscall.CloseHandle(h)
+               }
+               if err != tt.err {
+                       t.Errorf("%d: Open got %q, want %q", i, err, tt.err)
+               }
+       }
+}