mozapps/extensions/AddonContentPolicy.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "AddonContentPolicy.h"

#include "mozilla/dom/nsCSPUtils.h"
#include "nsCOMPtr.h"
#include "nsContentPolicyUtils.h"
#include "nsContentTypeParser.h"
#include "nsContentUtils.h"
#include "nsIConsoleService.h"
#include "nsIContentSecurityPolicy.h"
#include "nsIContent.h"
#include "nsIDocument.h"
#include "nsIEffectiveTLDService.h"
#include "nsIScriptError.h"
#include "nsIStringBundle.h"
#include "nsIUUIDGenerator.h"
#include "nsIURI.h"
#include "nsNetCID.h"
#include "nsNetUtil.h"

using namespace mozilla;

/* Enforces content policies for WebExtension scopes. Currently:
 *
 *  - Prevents loading scripts with a non-default JavaScript version.
 *  - Checks custom content security policies for sufficiently stringent
 *    script-src and object-src directives.
 */

#define VERSIONED_JS_BLOCKED_MESSAGE \
  u"Versioned JavaScript is a non-standard, deprecated extension, and is " \
  u"not supported in WebExtension code. For alternatives, please see: " \
  u"https://developer.mozilla.org/Add-ons/WebExtensions/Tips"

AddonContentPolicy::AddonContentPolicy()
{
}

AddonContentPolicy::~AddonContentPolicy()
{
}

NS_IMPL_ISUPPORTS(AddonContentPolicy, nsIContentPolicy, nsIAddonContentPolicy)

static nsresult
GetWindowIDFromContext(nsISupports* aContext, uint64_t *aResult)
{
  NS_ENSURE_TRUE(aContext, NS_ERROR_FAILURE);

  nsCOMPtr<nsIContent> content = do_QueryInterface(aContext);
  NS_ENSURE_TRUE(content, NS_ERROR_FAILURE);

  nsCOMPtr<nsIDocument> document = content->OwnerDoc();
  NS_ENSURE_TRUE(document, NS_ERROR_FAILURE);

  nsCOMPtr<nsPIDOMWindowInner> window = document->GetInnerWindow();
  NS_ENSURE_TRUE(window, NS_ERROR_FAILURE);

  *aResult = window->WindowID();
  return NS_OK;
}

static nsresult
LogMessage(const nsAString &aMessage, nsIURI* aSourceURI, const nsAString &aSourceSample,
           nsISupports* aContext)
{
  nsCOMPtr<nsIScriptError> error = do_CreateInstance(NS_SCRIPTERROR_CONTRACTID);
  NS_ENSURE_TRUE(error, NS_ERROR_OUT_OF_MEMORY);

  nsCString sourceName = aSourceURI->GetSpecOrDefault();

  uint64_t windowID = 0;
  GetWindowIDFromContext(aContext, &windowID);

  nsresult rv =
    error->InitWithWindowID(aMessage, NS_ConvertUTF8toUTF16(sourceName),
                            aSourceSample, 0, 0, nsIScriptError::errorFlag,
                            "JavaScript", windowID);
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIConsoleService> console = do_GetService(NS_CONSOLESERVICE_CONTRACTID);
  NS_ENSURE_TRUE(console, NS_ERROR_OUT_OF_MEMORY);

  console->LogMessage(error);
  return NS_OK;
}


// Content policy enforcement:

NS_IMETHODIMP
AddonContentPolicy::ShouldLoad(uint32_t aContentType,
                               nsIURI* aContentLocation,
                               nsIURI* aRequestOrigin,
                               nsISupports* aContext,
                               const nsACString& aMimeTypeGuess,
                               nsISupports* aExtra,
                               nsIPrincipal* aRequestPrincipal,
                               int16_t* aShouldLoad)
{
  MOZ_ASSERT(aContentType == nsContentUtils::InternalContentPolicyTypeToExternal(aContentType),
             "We should only see external content policy types here.");

  *aShouldLoad = nsIContentPolicy::ACCEPT;

  if (!aRequestOrigin) {
    return NS_OK;
  }

  // Only apply this policy to requests from documents loaded from
  // moz-extension URLs, or to resources being loaded from moz-extension URLs.
  bool equals;
  if (!((NS_SUCCEEDED(aContentLocation->SchemeIs("moz-extension", &equals)) && equals) ||
        (NS_SUCCEEDED(aRequestOrigin->SchemeIs("moz-extension", &equals)) && equals))) {
    return NS_OK;
  }

  if (aContentType == nsIContentPolicy::TYPE_SCRIPT) {
    NS_ConvertUTF8toUTF16 typeString(aMimeTypeGuess);
    nsContentTypeParser mimeParser(typeString);

    // Reject attempts to load JavaScript scripts with a non-default version.
    nsAutoString mimeType, version;
    if (NS_SUCCEEDED(mimeParser.GetType(mimeType)) &&
        nsContentUtils::IsJavascriptMIMEType(mimeType) &&
        NS_SUCCEEDED(mimeParser.GetParameter("version", version))) {
      *aShouldLoad = nsIContentPolicy::REJECT_REQUEST;

      LogMessage(NS_MULTILINE_LITERAL_STRING(VERSIONED_JS_BLOCKED_MESSAGE),
                 aRequestOrigin, typeString, aContext);
      return NS_OK;
    }
  }

  return NS_OK;
}

NS_IMETHODIMP
AddonContentPolicy::ShouldProcess(uint32_t aContentType,
                                  nsIURI* aContentLocation,
                                  nsIURI* aRequestOrigin,
                                  nsISupports* aRequestingContext,
                                  const nsACString& aMimeTypeGuess,
                                  nsISupports* aExtra,
                                  nsIPrincipal* aRequestPrincipal,
                                  int16_t* aShouldProcess)
{
  MOZ_ASSERT(aContentType == nsContentUtils::InternalContentPolicyTypeToExternal(aContentType),
             "We should only see external content policy types here.");

  *aShouldProcess = nsIContentPolicy::ACCEPT;
  return NS_OK;
}


// CSP Validation:

static const char* allowedSchemes[] = {
  "blob",
  "filesystem",
  nullptr
};

static const char* allowedHostSchemes[] = {
  "https",
  "moz-extension",
  nullptr
};

/**
 * Validates a CSP directive to ensure that it is sufficiently stringent.
 * In particular, ensures that:
 *
 *  - No remote sources are allowed other than from https: schemes
 *
 *  - No remote sources specify host wildcards for generic domains
 *    (*.blogspot.com, *.com, *)
 *
 *  - All remote sources and local extension sources specify a host
 *
 *  - No scheme sources are allowed other than blob:, filesystem:,
 *    moz-extension:, and https:
 *
 *  - No keyword sources are allowed other than 'none', 'self', 'unsafe-eval',
 *    and hash sources.
 */
class CSPValidator final : public nsCSPSrcVisitor {
  public:
    CSPValidator(nsAString& aURL, CSPDirective aDirective, bool aDirectiveRequired = true) :
      mURL(aURL),
      mDirective(CSP_CSPDirectiveToString(aDirective)),
      mFoundSelf(false)
    {
      // Start with the default error message for a missing directive, since no
      // visitors will be called if the directive isn't present.
      if (aDirectiveRequired) {
        FormatError("csp.error.missing-directive");
      }
    }

    // Visitors

    bool visitSchemeSrc(const nsCSPSchemeSrc& src) override
    {
      nsAutoString scheme;
      src.getScheme(scheme);

      if (SchemeInList(scheme, allowedHostSchemes)) {
        FormatError("csp.error.missing-host", scheme);
        return false;
      }
      if (!SchemeInList(scheme, allowedSchemes)) {
        FormatError("csp.error.illegal-protocol", scheme);
        return false;
      }
      return true;
    };

    bool visitHostSrc(const nsCSPHostSrc& src) override
    {
      nsAutoString scheme, host;

      src.getScheme(scheme);
      src.getHost(host);

      if (scheme.LowerCaseEqualsLiteral("https")) {
        if (!HostIsAllowed(host)) {
          FormatError("csp.error.illegal-host-wildcard", scheme);
          return false;
        }
      } else if (scheme.LowerCaseEqualsLiteral("moz-extension")) {
        // The CSP parser silently converts 'self' keywords to the origin
        // URL, so we need to reconstruct the URL to see if it was present.
        if (!mFoundSelf) {
          nsAutoString url(u"moz-extension://");
          url.Append(host);

          mFoundSelf = url.Equals(mURL);
        }

        if (host.IsEmpty() || host.EqualsLiteral("*")) {
          FormatError("csp.error.missing-host", scheme);
          return false;
        }
      } else if (!SchemeInList(scheme, allowedSchemes)) {
        FormatError("csp.error.illegal-protocol", scheme);
        return false;
      }

      return true;
    };

    bool visitKeywordSrc(const nsCSPKeywordSrc& src) override
    {
      switch (src.getKeyword()) {
      case CSP_NONE:
      case CSP_SELF:
      case CSP_UNSAFE_EVAL:
        return true;

      default:
        NS_ConvertASCIItoUTF16 keyword(CSP_EnumToKeyword(src.getKeyword()));

        FormatError("csp.error.illegal-keyword", keyword);
        return false;
      }
    };

    bool visitNonceSrc(const nsCSPNonceSrc& src) override
    {
      FormatError("csp.error.illegal-keyword", NS_LITERAL_STRING("'nonce-*'"));
      return false;
    };

    bool visitHashSrc(const nsCSPHashSrc& src) override
    {
      return true;
    };

    // Accessors

    inline nsAString& GetError()
    {
      return mError;
    };

    inline bool FoundSelf()
    {
      return mFoundSelf;
    };


    // Formatters

    template <typename... T>
    inline void FormatError(const char* aName, const T ...aParams)
    {
      const char16_t* params[] = { mDirective.get(), aParams.get()... };
      FormatErrorParams(aName, params, MOZ_ARRAY_LENGTH(params));
    };

  private:
    // Validators

    bool HostIsAllowed(nsAString& host)
    {
      if (host.First() == '*') {
        if (host.EqualsLiteral("*") || host[1] != '.') {
          return false;
        }

        host.Cut(0, 2);

        nsCOMPtr<nsIEffectiveTLDService> tldService =
          do_GetService(NS_EFFECTIVETLDSERVICE_CONTRACTID);

        if (!tldService) {
          return false;
        }

        NS_ConvertUTF16toUTF8 cHost(host);
        nsAutoCString publicSuffix;

        nsresult rv = tldService->GetPublicSuffixFromHost(cHost, publicSuffix);

        return NS_SUCCEEDED(rv) && !cHost.Equals(publicSuffix);
      }

      return true;
    };

    bool SchemeInList(nsAString& scheme, const char** schemes)
    {
      for (; *schemes; schemes++) {
        if (scheme.LowerCaseEqualsASCII(*schemes)) {
          return true;
        }
      }
      return false;
    };


    // Formatters

    already_AddRefed<nsIStringBundle>
    GetStringBundle()
    {
      nsCOMPtr<nsIStringBundleService> sbs =
        mozilla::services::GetStringBundleService();
      NS_ENSURE_TRUE(sbs, nullptr);

      nsCOMPtr<nsIStringBundle> stringBundle;
      sbs->CreateBundle("chrome://global/locale/extensions.properties",
                        getter_AddRefs(stringBundle));

      return stringBundle.forget();
    };

    void FormatErrorParams(const char* aName, const char16_t** aParams, int32_t aLength)
    {
      nsresult rv = NS_ERROR_FAILURE;

      nsCOMPtr<nsIStringBundle> stringBundle = GetStringBundle();

      if (stringBundle) {
        NS_ConvertASCIItoUTF16 name(aName);

        rv = stringBundle->FormatStringFromName(name.get(), aParams, aLength,
                                                getter_Copies(mError));
      }

      if (NS_WARN_IF(NS_FAILED(rv))) {
        mError.AssignLiteral("An unexpected error occurred");
      }
    };


    // Data members

    nsAutoString mURL;
    NS_ConvertASCIItoUTF16 mDirective;
    nsXPIDLString mError;

    bool mFoundSelf;
};

/**
 * Validates a custom content security policy string for use by an add-on.
 * In particular, ensures that:
 *
 *  - Both object-src and script-src directives are present, and meet
 *    the policies required by the CSPValidator class
 *
 *  - The script-src directive includes the source 'self'
 */
NS_IMETHODIMP
AddonContentPolicy::ValidateAddonCSP(const nsAString& aPolicyString,
                                     nsAString& aResult)
{
  nsresult rv;

  // Validate against a randomly-generated extension origin.
  // There is no add-on-specific behavior in the CSP code, beyond the ability
  // for add-ons to specify a custom policy, but the parser requires a valid
  // origin in order to operate correctly.
  nsAutoString url(u"moz-extension://");
  {
    nsCOMPtr<nsIUUIDGenerator> uuidgen = services::GetUUIDGenerator();
    NS_ENSURE_TRUE(uuidgen, NS_ERROR_FAILURE);

    nsID id;
    rv = uuidgen->GenerateUUIDInPlace(&id);
    NS_ENSURE_SUCCESS(rv, rv);

    char idString[NSID_LENGTH];
    id.ToProvidedString(idString);

    MOZ_RELEASE_ASSERT(idString[0] == '{' && idString[NSID_LENGTH - 2] == '}',
                       "UUID generator did not return a valid UUID");

    url.AppendASCII(idString + 1, NSID_LENGTH - 3);
  }


  RefPtr<BasePrincipal> principal =
    BasePrincipal::CreateCodebasePrincipal(NS_ConvertUTF16toUTF8(url));

  nsCOMPtr<nsIContentSecurityPolicy> csp;
  rv = principal->EnsureCSP(nullptr, getter_AddRefs(csp));
  NS_ENSURE_SUCCESS(rv, rv);


  csp->AppendPolicy(aPolicyString, false, false);

  const nsCSPPolicy* policy = csp->GetPolicy(0);
  if (!policy) {
    CSPValidator validator(url, nsIContentSecurityPolicy::SCRIPT_SRC_DIRECTIVE);
    aResult.Assign(validator.GetError());
    return NS_OK;
  }

  bool haveValidDefaultSrc = false;
  {
    CSPDirective directive = nsIContentSecurityPolicy::DEFAULT_SRC_DIRECTIVE;
    CSPValidator validator(url, directive);

    haveValidDefaultSrc = policy->visitDirectiveSrcs(directive, &validator);
  }

  aResult.SetIsVoid(true);
  {
    CSPDirective directive = nsIContentSecurityPolicy::SCRIPT_SRC_DIRECTIVE;
    CSPValidator validator(url, directive, !haveValidDefaultSrc);

    if (!policy->visitDirectiveSrcs(directive, &validator)) {
      aResult.Assign(validator.GetError());
    } else if (!validator.FoundSelf()) {
      validator.FormatError("csp.error.missing-source", NS_LITERAL_STRING("'self'"));
      aResult.Assign(validator.GetError());
    }
  }

  if (aResult.IsVoid()) {
    CSPDirective directive = nsIContentSecurityPolicy::OBJECT_SRC_DIRECTIVE;
    CSPValidator validator(url, directive, !haveValidDefaultSrc);

    if (!policy->visitDirectiveSrcs(directive, &validator)) {
      aResult.Assign(validator.GetError());
    }
  }

  return NS_OK;
}