fix: limit the plugin output size (notaryproject#484)

Fix:
- set the plugin output limit for STDOUT and STDERR to be 10MiB

Test:
- when the plugin output size exceeds 64MiB, the output pipe breaks, and
the plugin process outputs an error to STDERR

Spec changes: notaryproject/specifications#320
Resolves notaryproject#187

Signed-off-by: Junjie Gao <[email protected]>
Signed-off-by: Patrick Zheng <[email protected]>

internal/io/limitedwriter.go

@@ -0,0 +1,53 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package io provides a LimitWriter that writes to an underlying writer up to
+// a limit.
+
+package io
+
+import (
+	"errors"
+	"io"
+)
+
+// ErrLimitExceeded is returned when the write limit is exceeded.
+var ErrLimitExceeded = errors.New("write limit exceeded")
+
+// LimitedWriter is a writer that writes to an underlying writer up to a limit.
+type LimitedWriter struct {
+	W io.Writer // underlying writer
+	N int64     // remaining bytes
+}
+
+// LimitWriter returns a new LimitWriter that writes to w.
+//
+// parameters:
+// w: the writer to write to
+// limit: the maximum number of bytes to write
+func LimitWriter(w io.Writer, limit int64) *LimitedWriter {
+	return &LimitedWriter{W: w, N: limit}
+}
+
+// Write writes p to the underlying writer up to the limit.
+func (l *LimitedWriter) Write(p []byte) (int, error) {
+	if l.N <= 0 {
+		return 0, ErrLimitExceeded
+	}
+	if int64(len(p)) > l.N {
+		p = p[:l.N]
+	}
+	n, err := l.W.Write(p)
+	l.N -= int64(n)
+	return n, err
+}

internal/io/limitedwriter_test.go

@@ -0,0 +1,67 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package io
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+func TestLimitWriter(t *testing.T) {
+	limit := int64(10)
+
+	tests := []struct {
+		input    string
+		expected string
+		written  int
+	}{
+		{"hello", "hello", 5},
+		{" world", " world", 6},
+		{"!", "!", 1},
+		{"1234567891011", "1234567891", 10},
+	}
+
+	for _, tt := range tests {
+		var buf bytes.Buffer
+		lw := LimitWriter(&buf, limit)
+		n, err := lw.Write([]byte(tt.input))
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if n != tt.written {
+			t.Errorf("expected %d bytes written, got %d", tt.written, n)
+		}
+		if buf.String() != tt.expected {
+			t.Errorf("expected buffer %q, got %q", tt.expected, buf.String())
+		}
+	}
+}
+
+func TestLimitWriterFailed(t *testing.T) {
+	limit := int64(10)
+	longString := "1234567891011"
+
+	var buf bytes.Buffer
+	lw := LimitWriter(&buf, limit)
+	_, err := lw.Write([]byte(longString))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	_, err = lw.Write([]byte(longString))
+	expectedErr := errors.New("write limit exceeded")
+	if err.Error() != expectedErr.Error() {
+		t.Errorf("expected error %v, got %v", expectedErr, err)
+	}
+}

plugin/plugin.go

@@ -27,12 +27,16 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/notaryproject/notation-go/internal/io"
 	"github.com/notaryproject/notation-go/internal/slices"
 	"github.com/notaryproject/notation-go/log"
 	"github.com/notaryproject/notation-go/plugin/proto"
 	"github.com/notaryproject/notation-plugin-framework-go/plugin"
 )
 
+// maxPluginOutputSize is the maximum size of the plugin output.
+const maxPluginOutputSize = 64 * 1024 * 1024 // 64 MiB
+
 var executor commander = &execCommander{} // for unit test
 
 // GenericPlugin is the base requirement to be a plugin.
@@ -222,12 +226,14 @@ func (c execCommander) Output(ctx context.Context, name string, command plugin.C
 	var stdout, stderr bytes.Buffer
 	cmd := exec.CommandContext(ctx, name, string(command))
 	cmd.Stdin = bytes.NewReader(req)
-	cmd.Stderr = &stderr
-	cmd.Stdout = &stdout
+	// The limit writer will be handled by the caller in run() by comparing the
+	// bytes written with the expected length of the bytes.
+	cmd.Stderr = io.LimitWriter(&stderr, maxPluginOutputSize)
+	cmd.Stdout = io.LimitWriter(&stdout, maxPluginOutputSize)
 	err := cmd.Run()
 	if err != nil {
 		if errors.Is(ctx.Err(), context.DeadlineExceeded) {
-			return nil, stderr.Bytes(), fmt.Errorf("'%s %s' command execution timeout: %w", name, string(command), err);
+			return nil, stderr.Bytes(), fmt.Errorf("'%s %s' command execution timeout: %w", name, string(command), err)
 		}
 		return nil, stderr.Bytes(), err
 	}