fix: check binary size before decompression

pkg/workflows/wasm/host/module.go

@@ -75,6 +75,7 @@ var (
 	defaultMinMemoryMBs     = 128
 	DefaultInitialFuel      = uint64(100_000_000)
 	defaultMaxFetchRequests = 5
+	defaultMaxBinarySize    = 10 * 1024 * 1024 // 10 MB
 )
 
 type DeterminismConfig struct {
@@ -91,6 +92,7 @@ type ModuleConfig struct {
 	IsUncompressed   bool
 	Fetch            func(ctx context.Context, req *wasmpb.FetchRequest) (*wasmpb.FetchResponse, error)
 	MaxFetchRequests int
+	MaxBinarySize    int64
 
 	// Labeler is used to emit messages from the module.
 	Labeler custmsg.MessageEmitter
@@ -166,6 +168,10 @@ func NewModule(modCfg *ModuleConfig, binary []byte, opts ...func(*ModuleConfig))
 		modCfg.MinMemoryMBs = int64(defaultMinMemoryMBs)
 	}
 
+	if modCfg.MaxBinarySize == 0 {
+		modCfg.MaxBinarySize = int64(defaultMaxBinarySize)
+	}
+
 	// Take the max of the min and the configured max memory mbs.
 	// We do this because Go requires a minimum of 16 megabytes to run,
 	// and local testing has shown that with less than the min, some
@@ -183,6 +189,12 @@ func NewModule(modCfg *ModuleConfig, binary []byte, opts ...func(*ModuleConfig))
 
 	engine := wasmtime.NewEngineWithConfig(cfg)
 	if !modCfg.IsUncompressed {
+		// validate the binary size before decompressing
+		// this is to prevent decompression bombs
+		if int64(len(binary)) > modCfg.MaxBinarySize {
+			return nil, fmt.Errorf("binary size exceeds the maximum allowed size of %d bytes", modCfg.MaxBinarySize)
+		}
+
 		rdr := brotli.NewReader(bytes.NewBuffer(binary))
 		decompedBinary, err := io.ReadAll(rdr)
 		if err != nil {

pkg/workflows/wasm/host/wasm_test.go

@@ -903,6 +903,48 @@ func TestModule_Sandbox_Memory(t *testing.T) {
 	assert.ErrorContains(t, err, "exit status 2")
 }
 
+func TestModule_CompressedBinarySize(t *testing.T) {
+	t.Parallel()
+
+	t.Run("compressed binary size is smaller than the default 10mb limit", func(t *testing.T) {
+		binary := createTestBinary(successBinaryCmd, successBinaryLocation, false, t)
+
+		_, err := NewModule(&ModuleConfig{IsUncompressed: false, Logger: logger.Test(t)}, binary)
+		require.NoError(t, err)
+	})
+
+	t.Run("compressed binary size is bigger than the default 10mb limit", func(t *testing.T) {
+		// 11mb binary
+		binary := make([]byte, 11*1024*1024)
+
+		var b bytes.Buffer
+		bwr := brotli.NewWriter(&b)
+		_, err := bwr.Write(binary)
+		require.NoError(t, err)
+		require.NoError(t, bwr.Close())
+
+		_, err = NewModule(&ModuleConfig{IsUncompressed: false, Logger: logger.Test(t)}, binary)
+		default10mbLimit := fmt.Sprintf("binary size exceeds the maximum allowed size of %d bytes", 10*1024*1024)
+		require.ErrorContains(t, err, default10mbLimit)
+	})
+
+	t.Run("compressed binary size is bigger than the custom limit", func(t *testing.T) {
+		// 2mb binary
+		binary := make([]byte, 2*1024*1024)
+
+		var b bytes.Buffer
+		bwr := brotli.NewWriter(&b)
+		_, err := bwr.Write(binary)
+		require.NoError(t, err)
+		require.NoError(t, bwr.Close())
+
+		customMaxBinarySize := int64(1 * 1024 * 1024)
+		_, err = NewModule(&ModuleConfig{IsUncompressed: false, MaxBinarySize: customMaxBinarySize, Logger: logger.Test(t)}, binary)
+		default10mbLimit := fmt.Sprintf("binary size exceeds the maximum allowed size of %d bytes", customMaxBinarySize)
+		require.ErrorContains(t, err, default10mbLimit)
+	})
+}
+
 func TestModule_Sandbox_SleepIsStubbedOut(t *testing.T) {
 	t.Parallel()
 	ctx := tests.Context(t)