Fix prefix validation edge-case when extracting

Makefile

@@ -3,7 +3,7 @@
 
 
 SAMPLES_REPO ?= chainguard-dev/malcontent-samples
-SAMPLES_COMMIT ?= 528a7e975638d2c5ce06da1af32c5918aa4d6c7e
+SAMPLES_COMMIT ?= 2bd3bff19c0253821b3886db65a5059587cac893
 
 # BEGIN: lint-install ../malcontent
 # http://github.com/tinkerbell/lint-install

pkg/action/archive.go

@@ -48,6 +48,11 @@ func isSupportedArchive(path string) bool {
 	return archiveMap[getExt(path)]
 }
 
+// isValidPath checks if the target file is within the given directory.
+func isValidPath(target, dir string) bool {
+	return strings.HasPrefix(filepath.Clean(target), filepath.Clean(dir))
+}
+
 // getExt returns the extension of a file path
 // and attempts to avoid including fragments of filenames with other dots before the extension.
 func getExt(path string) string {
@@ -163,8 +168,8 @@ func extractTar(ctx context.Context, d string, f string) error {
 		}
 
 		target := filepath.Join(d, clean)
-		if !strings.HasPrefix(target, filepath.Clean(d)+string(os.PathSeparator)) {
-			return fmt.Errorf("invalid file path: %s", header.Name)
+		if !isValidPath(target, d) {
+			return fmt.Errorf("invalid file path: %s", target)
 		}
 
 		switch header.Typeflag {
@@ -206,7 +211,7 @@ func extractTar(ctx context.Context, d string, f string) error {
 			if err != nil {
 				return fmt.Errorf("failed to evaluate symlink: %w", err)
 			}
-			if !strings.HasPrefix(linkReal, filepath.Clean(d)+string(os.PathSeparator)) {
+			if !isValidPath(target, d) {
 				return fmt.Errorf("symlink points outside temporary directory: %s", linkReal)
 			}
 			if err := os.Symlink(linkReal, target); err != nil {
@@ -281,8 +286,8 @@ func extractZip(ctx context.Context, d string, f string) error {
 		}
 
 		name := filepath.Join(d, clean)
-		if !strings.HasPrefix(name, filepath.Clean(d)+string(os.PathSeparator)) {
-			logger.Warnf("skipping file path outside extraction directory: %s", file.Name)
+		if !isValidPath(name, d) {
+			logger.Warnf("skipping file path outside extraction directory: %s", name)
 			continue
 		}
 
@@ -494,7 +499,7 @@ func extractDeb(ctx context.Context, d, f string) error {
 			if err != nil {
 				return fmt.Errorf("failed to evaluate symlink: %w", err)
 			}
-			if !strings.HasPrefix(linkReal, filepath.Clean(d)+string(os.PathSeparator)) {
+			if !isValidPath(linkReal, d) {
 				return fmt.Errorf("symlink points outside temporary directory: %s", linkReal)
 			}
 			if err := os.Symlink(linkReal, target); err != nil {

pkg/action/archive_test.go

@@ -7,6 +7,7 @@
 	"os"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"testing"
 
 	"github.com/chainguard-dev/clog"
@@ -330,3 +331,81 @@
 		})
 	}
 }
+
+func TestIsValidPath(t *testing.T) {
+	tmpRoot, err := os.MkdirTemp("", "isValidPath-*")
+	if err != nil {
+		t.Fatalf("Failed to create temp base directory: %v", err)
+	}
+	defer os.RemoveAll(tmpRoot)
+
+	tempSubDir, err := os.MkdirTemp(tmpRoot, "isValidPathSub-*")
+	if err != nil {
+		t.Fatalf("Failed to create temp sub directory: %v", err)
+	}
+
+	tests := []struct {
+		name     string
+		target   string
+		baseDir  string
+		expected bool
+	}{
+		{
+			name:     "Valid direct child path",
+			target:   filepath.Join(tmpRoot, "file.txt"),
+			baseDir:  tmpRoot,
+			expected: true,
+		},
+		{
+			name:     "Valid nested path",
+			target:   filepath.Join(tempSubDir, "file.txt"),
+			baseDir:  tmpRoot,
+			expected: true,
+		},
+		{
+			name:     "Invalid parent directory traversal",
+			target:   filepath.Join(tmpRoot, "../file.txt"),
+			baseDir:  tmpRoot,
+			expected: false,
+		},
+		{
+			name:     "Invalid absolute path outside base",
+			target:   "/etc/passwd",
+			baseDir:  tmpRoot,
+			expected: false,
+		},
+		{
+			name:     "Invalid relative path outside base",
+			target:   "../../etc/passwd",
+			baseDir:  tmpRoot,
+			expected: false,
+		},
+		{
+			name:     "Empty target path",
+			target:   "",
+			baseDir:  tmpRoot,
+			expected: false,
+		},
+		{
+			name:     "Empty base directory",
+			target:   filepath.Join(tmpRoot, "file.txt"),
+			baseDir:  "",
+			expected: false,
+		},
+		{
+			name:     "Path with irregular separators",
+			target:   strings.Replace(filepath.Join(tmpRoot, "file.txt"), "/", "//", -1),
+			baseDir:  tmpRoot,
+			expected: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isValidPath(tt.target, tt.baseDir)
+			if result != tt.expected {
+				t.Errorf("isValidPath(%q, %q) = %v, want %v", tt.target, tt.baseDir, result, tt.expected)
+			}
+		})
+	}
+}