From 301943c3a5eabba87a7f21c9545ece3defcb828b Mon Sep 17 00:00:00 2001
From: Felicitas Pojtinger <felicitas@pojtinger.com>
Date: Fri, 21 Jan 2022 01:12:05 +0100
Subject: [PATCH] fix: Prevent creating files in place of symlinks to
 directories

---
 pkg/fs/filesystem.go      | 16 +++++--
 pkg/fs/filesystem_test.go | 96 +++++++++++++++++++++++++++++++++++----
 2 files changed, 100 insertions(+), 12 deletions(-)

diff --git a/pkg/fs/filesystem.go b/pkg/fs/filesystem.go
index 7ff54b7..9a307b6 100644
--- a/pkg/fs/filesystem.go
+++ b/pkg/fs/filesystem.go
@@ -78,9 +78,6 @@ func (f *STFS) Name() string {
 		"name": config.FileSystemNameSTFS,
 	})
 
-	f.ioLock.Lock()
-	defer f.ioLock.Unlock()
-
 	return config.FileSystemNameSTFS
 }
 
@@ -442,6 +439,19 @@ func (f *STFS) OpenFile(name string, flag int, perm os.FileMode) (afero.File, er
 					return nil, err
 				}
 
+				if target, err := inventory.Stat(
+					f.metadata,
+
+					name,
+					true,
+
+					f.onHeader,
+				); err == nil {
+					if target.Typeflag == tar.TypeDir {
+						return nil, config.ErrIsDirectory
+					}
+				}
+
 				if err := f.mknodeWithoutLocking(false, name, perm, false, "", false); err != nil {
 					return nil, err
 				}
diff --git a/pkg/fs/filesystem_test.go b/pkg/fs/filesystem_test.go
index 19f44e8..e260716 100644
--- a/pkg/fs/filesystem_test.go
+++ b/pkg/fs/filesystem_test.go
@@ -656,36 +656,103 @@ var createTests = []struct {
 	name    string
 	args    createArgs
 	wantErr bool
+	prepare func(symFs) error
 }{
 	{
 		"Can create file /test.txt",
 		createArgs{"/test.txt"},
 		false,
+		func(sf symFs) error { return nil },
 	},
 	{
 		"Can create file /test.txt/",
 		createArgs{"/test.txt/"},
 		false,
+		func(sf symFs) error { return nil },
 	},
 	{
-		"Can not create existing file/directory /",
+		"Can not create existing file /",
 		createArgs{"/"},
 		true,
+		func(sf symFs) error { return nil },
 	},
 	{
 		"Can create file ' '",
 		createArgs{" "},
 		false,
+		func(sf symFs) error { return nil },
 	},
 	{
 		"Can create file ''",
 		createArgs{""},
 		true,
+		func(sf symFs) error { return nil },
 	},
 	{
 		"Can not create /nonexistent/test.txt",
 		createArgs{"/nonexistent/test.txt"},
 		true,
+		func(sf symFs) error { return nil },
+	},
+	{
+		"Can not create file in place of symlink to root",
+		createArgs{"/existingsymlink"},
+		true,
+		func(sf symFs) error {
+			if err := sf.SymlinkIfPossible("/", "/existingsymlink"); err != nil {
+				return nil
+			}
+
+			return nil
+		},
+	},
+	{
+		"Can create file in place of broken symlink /brokensymlink",
+		createArgs{"/brokensymlink"},
+		false,
+		func(sf symFs) error {
+			if err := sf.SymlinkIfPossible("/test.txt", "/brokensymlink"); err != nil {
+				return nil
+			}
+
+			return nil
+		},
+	},
+	{
+		"Can create file in place of existing symlink /existingsymlink to file",
+		createArgs{"/existingsymlink"},
+		false,
+		func(sf symFs) error {
+			file, err := sf.Create("/test.txt")
+			if err != nil {
+				return err
+			}
+			if err := file.Close(); err != nil {
+				return err
+			}
+
+			if err := sf.SymlinkIfPossible("/test.txt", "/existingsymlink"); err != nil {
+				return nil
+			}
+
+			return nil
+		},
+	},
+	{
+		"Can not create file in place of existing symlink /existingsymlink to directory",
+		createArgs{"/existingsymlink"},
+		true,
+		func(sf symFs) error {
+			if err := sf.Mkdir("/mydir", os.ModePerm); err != nil {
+				return err
+			}
+
+			if err := sf.SymlinkIfPossible("/mydir", "/existingsymlink"); err != nil {
+				return nil
+			}
+
+			return nil
+		},
 	},
 }
 
@@ -694,36 +761,47 @@ func TestSTFS_Create(t *testing.T) {
 		tt := tt
 
 		runTestForAllFss(t, tt.name, true, true, true, func(t *testing.T, fs fsConfig) {
-			file, err := fs.fs.Create(tt.args.name)
+			symFs, ok := fs.fs.(symFs)
+			if !ok {
+				return
+			}
+
+			if err := tt.prepare(symFs); err != nil {
+				t.Errorf("%v prepare() error = %v", symFs.Name(), err)
+
+				return
+			}
+
+			file, err := symFs.Create(tt.args.name)
 			if (err != nil) != tt.wantErr {
-				t.Errorf("%v.Create() error = %v, wantErr %v", fs.fs.Name(), err, tt.wantErr)
+				t.Errorf("%v.Create() error = %v, wantErr %v", symFs.Name(), err, tt.wantErr)
 
 				return
 			}
 
 			if !tt.wantErr {
-				want, err := fs.fs.Stat(tt.args.name)
+				want, err := symFs.Stat(tt.args.name)
 				if err != nil {
-					t.Errorf("%v.Stat() error = %v, wantErr %v", fs.fs.Name(), err, tt.wantErr)
+					t.Errorf("%v.Stat() error = %v, wantErr %v", symFs.Name(), err, tt.wantErr)
 
 					return
 				}
 
 				if file == nil {
-					t.Errorf("%v.Create() error = %v, wantErr %v", fs.fs.Name(), err, tt.wantErr)
+					t.Errorf("%v.Create() error = %v, wantErr %v", symFs.Name(), err, tt.wantErr)
 
 					return
 				}
 
-				got, err := fs.fs.Stat(file.Name())
+				got, err := symFs.Stat(file.Name())
 				if err != nil {
-					t.Errorf("%v.Stat() error = %v, wantErr %v", fs.fs.Name(), err, tt.wantErr)
+					t.Errorf("%v.Stat() error = %v, wantErr %v", symFs.Name(), err, tt.wantErr)
 
 					return
 				}
 
 				if !reflect.DeepEqual(got, want) {
-					t.Errorf("%v.Create().Name() = %v, want %v", fs.fs.Name(), got, want)
+					t.Errorf("%v.Create().Name() = %v, want %v", symFs.Name(), got, want)
 
 					return
 				}