syscallcompat: add OpenNofollow helper

OpenNofollow = symlink-race-safe Open

Prepares fixing https://github.com/rfjakob/gocryptfs/issues/165

1 files changed, 37 insertions, 0 deletions

diff --git a/internal/syscallcompat/open_nofollow_test.go b/internal/syscallcompat/open_nofollow_test.go
new file mode 100644
index 0000000..e9cdf77
--- /dev/null
+++ b/internal/syscallcompat/open_nofollow_test.go
@@ -0,0 +1,37 @@
+package syscallcompat
+
+import (
+	"os"
+	"syscall"
+	"testing"
+)
+
+func TestOpenNofollow(t *testing.T) {
+	err := os.MkdirAll(tmpDir+"/d1/d2/d3", 0700)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Create a file
+	fd, err := OpenNofollow(tmpDir, "d1/d2/d3/f1", syscall.O_RDWR|syscall.O_CREAT|syscall.O_EXCL, 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	syscall.Close(fd)
+	_, err = os.Stat(tmpDir + "/d1/d2/d3/f1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Replace "d1" with a symlink - open should fail with ELOOP
+	err = os.Rename(tmpDir+"/d1", tmpDir+"/d1.renamed")
+	if err != nil {
+		t.Fatal(err)
+	}
+	os.Symlink(tmpDir+"/d1.renamed", tmpDir+"/d1")
+	fd, err = OpenNofollow(tmpDir, "d1/d2/d3/f1", syscall.O_RDWR|syscall.O_CREAT, 0600)
+	if err == nil {
+		t.Fatalf("should have failed")
+	}
+	if err != syscall.ELOOP {
+		t.Errorf("expected ELOOP, got %v", err)
+	}
+}