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os: use O_EXCL instead of O_TRUNC in CopyFS to disallow rewriting existing files

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On Linux, a call to creat() is equivalent to calling open() with flags
equal to O_CREAT|O_WRONLY|O_TRUNC, which applies to other platforms
as well in a similar manner. Thus, to force CopyFS's behavior to
comply with the function comment, we need to replace O_TRUNC with O_EXCL.

Fixes #68895

Change-Id: I3e2ab153609d3c8cf20ce5969d6f3ef593833cd1
Reviewed-on: https://go-review.googlesource.com/c/go/+/606095
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
This commit is contained in:
Andy Pan 2024-08-16 08:04:57 +08:00 committed by Gopher Robot
parent 660e7d60f2
commit aa5d672a00
2 changed files with 20 additions and 3 deletions
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7
src/os/dir.go
View File

@ -136,8 +136,9 @@ func ReadDir(name string) ([]DirEntry, error) {
// from the source, and directories are created with mode 0o777
// (before umask).
//
// CopyFS will not overwrite existing files, and returns an error
// if a file name in fsys already exists in the destination.
// CopyFS will not overwrite existing files. If a file name in fsys
// already exists in the destination, CopyFS will return an error
// such that errors.Is(err, fs.ErrExist) will be true.
//
// Symbolic links in fsys are not supported. A *PathError with Err set
// to ErrInvalid is returned when copying from a symbolic link.
@ -176,7 +177,7 @@ func CopyFS(dir string, fsys fs.FS) error {
if err != nil {
return err
}
w, err := OpenFile(newPath, O_CREATE|O_TRUNC|O_WRONLY, 0666|info.Mode()&0777)
w, err := OpenFile(newPath, O_CREATE|O_EXCL|O_WRONLY, 0666|info.Mode()&0777)
if err != nil {
return err
}

16
src/os/os_test.go
View File

@ -3407,6 +3407,14 @@ func TestCopyFS(t *testing.T) {
t.Fatal("comparing two directories:", err)
}
// Test whether CopyFS disallows copying for disk filesystem when there is any
// existing file in the destination directory.
if err := CopyFS(tmpDir, fsys); !errors.Is(err, fs.ErrExist) {
t.Errorf("CopyFS should have failed and returned error when there is"+
"any existing file in the destination directory (in disk filesystem), "+
"got: %v, expected any error that indicates <file exists>", err)
}
// Test with memory filesystem.
fsys = fstest.MapFS{
"william": {Data: []byte("Shakespeare\n")},
@ -3444,6 +3452,14 @@ func TestCopyFS(t *testing.T) {
}); err != nil {
t.Fatal("comparing two directories:", err)
}
// Test whether CopyFS disallows copying for memory filesystem when there is any
// existing file in the destination directory.
if err := CopyFS(tmpDir, fsys); !errors.Is(err, fs.ErrExist) {
t.Errorf("CopyFS should have failed and returned error when there is"+
"any existing file in the destination directory (in memory filesystem), "+
"got: %v, expected any error that indicates <file exists>", err)
}
}
func TestCopyFSWithSymlinks(t *testing.T) {