securityConfig.go

// Copyright 2018 The Hugo Authors. All rights reserved.
//
// 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 security

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"reflect"
	"strings"

	"github.com/gohugoio/hugo/common/herrors"
	"github.com/gohugoio/hugo/common/types"
	"github.com/gohugoio/hugo/config"
	"github.com/gohugoio/hugo/parser"
	"github.com/gohugoio/hugo/parser/metadecoders"
	"github.com/mitchellh/mapstructure"
)

const securityConfigKey = "security"

// DefaultConfig holds the default security policy.
var DefaultConfig = Config{
	Exec: Exec{
		Allow: NewWhitelist(
			"^dart-sass-embedded$",
			"^go$",  // for Go Modules
			"^npx$", // used by all Node tools (Babel, PostCSS).
			"^postcss$",
		),
		// These have been tested to work with Hugo's external programs
		// on Windows, Linux and MacOS.
		OsEnv: NewWhitelist("(?i)^(PATH|PATHEXT|APPDATA|TMP|TEMP|TERM)$"),
	},
	Funcs: Funcs{
		Getenv: NewWhitelist("^HUGO_"),
	},
	HTTP: HTTP{
		URLs:    NewWhitelist(".*"),
		Methods: NewWhitelist("(?i)GET|POST"),
	},
}

// Config is the top level security config.
type Config struct {
	// Restricts access to os.Exec.
	Exec Exec `json:"exec"`

	// Restricts access to certain template funcs.
	Funcs Funcs `json:"funcs"`

	// Restricts access to resources.Get, getJSON, getCSV.
	HTTP HTTP `json:"http"`

	// Allow inline shortcodes
	EnableInlineShortcodes bool `json:"enableInlineShortcodes"`
}

// Exec holds os/exec policies.
type Exec struct {
	Allow Whitelist `json:"allow"`
	OsEnv Whitelist `json:"osEnv"`
}

// Funcs holds template funcs policies.
type Funcs struct {
	// OS env keys allowed to query in os.Getenv.
	Getenv Whitelist `json:"getenv"`
}

type HTTP struct {
	// URLs to allow in remote HTTP (resources.Get, getJSON, getCSV).
	URLs Whitelist `json:"urls"`

	// HTTP methods to allow.
	Methods Whitelist `json:"methods"`
}

// ToTOML converts c to TOML with [security] as the root.
func (c Config) ToTOML() string {
	sec := c.ToSecurityMap()

	var b bytes.Buffer

	if err := parser.InterfaceToConfig(sec, metadecoders.TOML, &b); err != nil {
		panic(err)
	}

	return strings.TrimSpace(b.String())
}

func (c Config) CheckAllowedExec(name string) error {
	if !c.Exec.Allow.Accept(name) {
		return &AccessDeniedError{
			name:     name,
			path:     "security.exec.allow",
			policies: c.ToTOML(),
		}
	}
	return nil

}

func (c Config) CheckAllowedGetEnv(name string) error {
	if !c.Funcs.Getenv.Accept(name) {
		return &AccessDeniedError{
			name:     name,
			path:     "security.funcs.getenv",
			policies: c.ToTOML(),
		}
	}
	return nil
}

func (c Config) CheckAllowedHTTPURL(url string) error {
	if !c.HTTP.URLs.Accept(url) {
		return &AccessDeniedError{
			name:     url,
			path:     "security.http.urls",
			policies: c.ToTOML(),
		}
	}
	return nil
}

func (c Config) CheckAllowedHTTPMethod(method string) error {
	if !c.HTTP.Methods.Accept(method) {
		return &AccessDeniedError{
			name:     method,
			path:     "security.http.method",
			policies: c.ToTOML(),
		}
	}
	return nil
}

// ToSecurityMap converts c to a map with 'security' as the root key.
func (c Config) ToSecurityMap() map[string]interface{} {
	// Take it to JSON and back to get proper casing etc.
	asJson, err := json.Marshal(c)
	herrors.Must(err)
	m := make(map[string]interface{})
	herrors.Must(json.Unmarshal(asJson, &m))

	// Add the root
	sec := map[string]interface{}{
		"security": m,
	}
	return sec

}

// DecodeConfig creates a privacy Config from a given Hugo configuration.
func DecodeConfig(cfg config.Provider) (Config, error) {
	sc := DefaultConfig
	if cfg.IsSet(securityConfigKey) {
		m := cfg.GetStringMap(securityConfigKey)
		dec, err := mapstructure.NewDecoder(
			&mapstructure.DecoderConfig{
				WeaklyTypedInput: true,
				Result:           &sc,
				DecodeHook:       stringSliceToWhitelistHook(),
			},
		)
		if err != nil {
			return sc, err
		}

		if err = dec.Decode(m); err != nil {
			return sc, err
		}
	}

	if !sc.EnableInlineShortcodes {
		// Legacy
		sc.EnableInlineShortcodes = cfg.GetBool("enableInlineShortcodes")
	}

	return sc, nil

}

func stringSliceToWhitelistHook() mapstructure.DecodeHookFuncType {
	return func(
		f reflect.Type,
		t reflect.Type,
		data interface{}) (interface{}, error) {

		if t != reflect.TypeOf(Whitelist{}) {
			return data, nil
		}

		wl := types.ToStringSlicePreserveString(data)

		return NewWhitelist(wl...), nil

	}
}

// AccessDeniedError represents a security policy conflict.
type AccessDeniedError struct {
	path     string
	name     string
	policies string
}

func (e *AccessDeniedError) Error() string {
	return fmt.Sprintf("access denied: %q is not whitelisted in policy %q; the current security configuration is:\n\n%s\n\n", e.name, e.path, e.policies)
}

// IsAccessDenied reports whether err is an AccessDeniedError
func IsAccessDenied(err error) bool {
	var notFoundErr *AccessDeniedError
	return errors.As(err, &notFoundErr)
}