darwin: syscallcompat: Openat: use O_SYMLINKo_symlink

Also add tests that opening a symlink (using unix.O_PATH | unix.O_NOFOLLOW)
works.

https://github.com/rfjakob/gocryptfs/issues/993

2 files changed, 83 insertions, 0 deletions

diff --git a/tests/matrix/symlink_darwin_test.go b/tests/matrix/symlink_darwin_test.go
new file mode 100644
index 0000000..b8284a5
--- /dev/null
+++ b/tests/matrix/symlink_darwin_test.go
@@ -0,0 +1,38 @@
+package matrix
+
+import (
+	"os"
+	"testing"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/rfjakob/gocryptfs/v2/tests/test_helpers"
+)
+
+// Darwin has O_SYMLINK which is more powerful than O_NOFOLLOW
+func TestOpenSymlinkDarwin(t *testing.T) {
+	path := test_helpers.DefaultPlainDir + "/TestOpenSymlink"
+	target := "/target/does/not/exist"
+	err := os.Symlink(target, path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	fd, err := unix.Open(path, unix.O_RDONLY|unix.O_SYMLINK, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Close(fd)
+	var st unix.Stat_t
+	if err := unix.Fstat(fd, &st); err != nil {
+		t.Fatal(err)
+	}
+	if st.Size != int64(len(target)) {
+		t.Errorf("wrong size: have=%d want=%d", st.Size, len(target))
+	}
+	if err := unix.Unlink(path); err != nil {
+		t.Fatal(err)
+	}
+	if err := unix.Fstat(fd, &st); err != nil {
+		t.Error(err)
+	}
+}
diff --git a/tests/matrix/symlink_linux_test.go b/tests/matrix/symlink_linux_test.go
new file mode 100644
index 0000000..e0deb43
--- /dev/null
+++ b/tests/matrix/symlink_linux_test.go
@@ -0,0 +1,45 @@
+package matrix
+
+import (
+	"os"
+	"testing"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/rfjakob/gocryptfs/v2/tests/test_helpers"
+)
+
+// TestOpenSymlink only works on Linux because is uses
+// O_PATH and AT_EMPTY_PATH. These do not exist on MacOS.
+func TestOpenSymlinkLinux(t *testing.T) {
+	path := test_helpers.DefaultPlainDir + "/TestOpenSymlink"
+	target := "/target/does/not/exist"
+	err := os.Symlink(target, path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	how := unix.OpenHow{
+		Flags: unix.O_PATH | unix.O_NOFOLLOW,
+	}
+	fd, err := unix.Openat2(unix.AT_FDCWD, path, &how)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Close(fd)
+	var st unix.Stat_t
+	if err := unix.Fstatat(fd, "", &st, unix.AT_EMPTY_PATH); err != nil {
+		t.Fatal(err)
+	}
+	if st.Size != int64(len(target)) {
+		t.Errorf("wrong size: have=%d want=%d", st.Size, len(target))
+	}
+	if err := unix.Unlink(path); err != nil {
+		t.Fatal(err)
+	}
+	if err = unix.Fstatat(fd, "", &st, unix.AT_EMPTY_PATH); err != nil {
+		// That's a bug, but I have never heard of a use case that would break because of this.
+		// Also I don't see how to fix it, as gocryptfs does not get informed about the earlier
+		// Openat2().
+		t.Logf("posix compliance issue: deleted symlink cannot be accessed: Fstatat: %v", err)
+	}
+}