From 5dc3220ee0d92c5830b5e4df9f8ad5dafe374e9c Mon Sep 17 00:00:00 2001
From: Aryan <aryangupta050903@gmail.com>
Date: Sat, 17 Oct 2026 00:12:18 +0530
Subject: [PATCH] memfs: Reject ReadDir calls on regular files

Returning an empty directory listing for a regular file hides invalid
paths from callers and differs from the OS-backed filesystem. Check the
target mode after resolving symlinks and return a PathError wrapping
ENOTDIR.

Add a shared filesystem regression and memfs coverage for symlinks to
files and directories.

Assisted-by: OpenAI Codex (GPT-6)
Signed-off-by: Aryan <aryangupta050903@gmail.com>
---
 memfs/memory.go      |  3 +++
 memfs/memory_test.go | 16 ++++++++++++++++
 test/dir_test.go     | 15 +++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/memfs/memory.go b/memfs/memory.go
index 3c700d6..9798cc5 100644
--- a/memfs/memory.go
+++ b/memfs/memory.go
@@ -171,6 +171,9 @@ func (fs *Memory) ReadDir(path string) ([]gofs.DirEntry, error) {
 				return fs.ReadDir(target)
 			}
 		}
+		if !f.mode.IsDir() {
+			return nil, &os.PathError{Op: "readdir", Path: path, Err: syscall.ENOTDIR}
+		}
 	} else {
 		return nil, &os.PathError{Op: "open", Path: path, Err: syscall.ENOENT}
 	}
diff --git a/memfs/memory_test.go b/memfs/memory_test.go
index c07d52f..4fab871 100644
--- a/memfs/memory_test.go
+++ b/memfs/memory_test.go
@@ -137,6 +137,22 @@ func TestNotFound(t *testing.T) {
 	assert.ErrorIs(t, err, os.ErrNotExist)
 }
 
+func TestReadDirSymlink(t *testing.T) {
+	fs := New()
+	require.NoError(t, util.WriteFile(fs, "file", nil, 0o644))
+	require.NoError(t, fs.MkdirAll("dir", 0o755))
+	require.NoError(t, fs.Symlink("file", "file-link"))
+	require.NoError(t, fs.Symlink("dir", "dir-link"))
+
+	entries, err := fs.ReadDir("file-link")
+	require.ErrorIs(t, err, syscall.ENOTDIR)
+	assert.Nil(t, entries)
+
+	entries, err = fs.ReadDir("dir-link")
+	require.NoError(t, err)
+	assert.Empty(t, entries)
+}
+
 func TestTruncateAppend(t *testing.T) {
 	fs := New()
 	err := util.WriteFile(fs, "truncate_append", []byte("file-content"), 0o666)
diff --git a/test/dir_test.go b/test/dir_test.go
index 0f98f26..1b0bcac 100644
--- a/test/dir_test.go
+++ b/test/dir_test.go
@@ -169,6 +169,21 @@ func TestDir_ReadDir(t *testing.T) {
 	})
 }
 
+func TestDir_ReadDirFile(t *testing.T) {
+	eachDirFS(t, func(t *testing.T, fs dirFS) {
+		t.Helper()
+		err := util.WriteFile(fs, "dir/file", []byte("content"), 0o644)
+		require.NoError(t, err)
+
+		entries, err := fs.ReadDir("dir/file")
+		require.Error(t, err)
+		assert.Nil(t, entries)
+
+		var pathErr *os.PathError
+		require.ErrorAs(t, err, &pathErr)
+	})
+}
+
 func TestDir_ReadDirNested(t *testing.T) {
 	eachDirFS(t, func(t *testing.T, fs dirFS) {
 		t.Helper()