gecko-dev/dom/canvas/CanvasUtils.cpp

/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 <stdlib.h>
#include <stdarg.h>

#include "nsICanvasRenderingContextInternal.h"
#include "nsIHTMLCollection.h"
#include "mozilla/dom/BrowserChild.h"
#include "mozilla/dom/Document.h"
#include "mozilla/dom/HTMLCanvasElement.h"
#include "mozilla/dom/UserActivation.h"
#include "mozilla/dom/WorkerCommon.h"
#include "mozilla/dom/WorkerPrivate.h"
#include "mozilla/gfx/gfxVars.h"
#include "mozilla/BasePrincipal.h"
#include "mozilla/StaticPrefs_gfx.h"
#include "mozilla/StaticPrefs_privacy.h"
#include "mozilla/StaticPrefs_webgl.h"
#include "nsIPrincipal.h"

#include "nsGfxCIID.h"

#include "nsTArray.h"

#include "CanvasUtils.h"
#include "mozilla/gfx/Matrix.h"
#include "WebGL2Context.h"

#include "nsIScriptError.h"
#include "nsIScriptObjectPrincipal.h"
#include "nsIPermissionManager.h"
#include "nsIObserverService.h"
#include "mozilla/Services.h"
#include "mozIThirdPartyUtil.h"
#include "nsContentUtils.h"
#include "nsUnicharUtils.h"
#include "nsPrintfCString.h"
#include "jsapi.h"

#define TOPIC_CANVAS_PERMISSIONS_PROMPT "canvas-permissions-prompt"
#define TOPIC_CANVAS_PERMISSIONS_PROMPT_HIDE_DOORHANGER \
  "canvas-permissions-prompt-hide-doorhanger"
#define PERMISSION_CANVAS_EXTRACT_DATA "canvas"_ns

using namespace mozilla::gfx;

namespace mozilla::CanvasUtils {

bool IsImageExtractionAllowed(dom::Document* aDocument, JSContext* aCx,
                              Maybe<nsIPrincipal*> aPrincipal) {
  // Do the rest of the checks only if privacy.resistFingerprinting is on.
  if (!nsContentUtils::ShouldResistFingerprinting(aDocument)) {
    return true;
  }

  // Don't proceed if we don't have a document or JavaScript context.
  if (!aDocument || !aCx || !aPrincipal) {
    return false;
  }

  nsIPrincipal& subjectPrincipal = *aPrincipal.ref();

  // The system principal can always extract canvas data.
  if (subjectPrincipal.IsSystemPrincipal()) {
    return true;
  }

  // Allow extension principals.
  auto* principal = BasePrincipal::Cast(&subjectPrincipal);
  if (principal->AddonPolicy() || principal->ContentScriptAddonPolicy()) {
    return true;
  }

  // Get the document URI and its spec.
  nsIURI* docURI = aDocument->GetDocumentURI();
  nsCString docURISpec;
  docURI->GetSpec(docURISpec);

  // Allow local files to extract canvas data.
  if (docURI->SchemeIs("file")) {
    return true;
  }

  // Don't show canvas prompt for PDF.js
  JS::AutoFilename scriptFile;
  if (JS::DescribeScriptedCaller(aCx, &scriptFile) && scriptFile.get() &&
      strcmp(scriptFile.get(), "resource://pdf.js/build/pdf.js") == 0) {
    return true;
  }

  // Block all third-party attempts to extract canvas.
  MOZ_ASSERT(aDocument->GetWindowContext());
  bool isThirdParty =
      aDocument->GetWindowContext()
          ? aDocument->GetWindowContext()->GetIsThirdPartyWindow()
          : false;
  if (isThirdParty) {
    nsAutoString message;
    message.AppendPrintf("Blocked third party %s from extracting canvas data.",
                         docURISpec.get());
    nsContentUtils::ReportToConsoleNonLocalized(
        message, nsIScriptError::warningFlag, "Security"_ns, aDocument);
    return false;
  }

  // Load Permission Manager service.
  nsresult rv;
  nsCOMPtr<nsIPermissionManager> permissionManager =
      do_GetService(NS_PERMISSIONMANAGER_CONTRACTID, &rv);
  NS_ENSURE_SUCCESS(rv, false);

  // Check if the site has permission to extract canvas data.
  // Either permit or block extraction if a stored permission setting exists.
  uint32_t permission;
  rv = permissionManager->TestPermissionFromPrincipal(
      principal, PERMISSION_CANVAS_EXTRACT_DATA, &permission);
  NS_ENSURE_SUCCESS(rv, false);
  switch (permission) {
    case nsIPermissionManager::ALLOW_ACTION:
      return true;
    case nsIPermissionManager::DENY_ACTION:
      return false;
    default:
      break;
  }

  // At this point, permission is unknown
  // (nsIPermissionManager::UNKNOWN_ACTION).

  // Check if the request is in response to user input
  bool isAutoBlockCanvas =
      StaticPrefs::
          privacy_resistFingerprinting_autoDeclineNoUserInputCanvasPrompts() &&
      !dom::UserActivation::IsHandlingUserInput();

  if (isAutoBlockCanvas) {
    nsAutoString message;
    message.AppendPrintf(
        "Blocked %s from extracting canvas data because no user input was "
        "detected.",
        docURISpec.get());
    nsContentUtils::ReportToConsoleNonLocalized(
        message, nsIScriptError::warningFlag, "Security"_ns, aDocument);
  } else {
    // It was in response to user input, so log and display the prompt.
    nsAutoString message;
    message.AppendPrintf(
        "Blocked %s from extracting canvas data, but prompting the user.",
        docURISpec.get());
    nsContentUtils::ReportToConsoleNonLocalized(
        message, nsIScriptError::warningFlag, "Security"_ns, aDocument);
  }

  // Prompt the user (asynchronous).
  nsPIDOMWindowOuter* win = aDocument->GetWindow();
  nsAutoCString origin;
  rv = principal->GetOrigin(origin);
  NS_ENSURE_SUCCESS(rv, false);

  if (XRE_IsContentProcess()) {
    dom::BrowserChild* browserChild = dom::BrowserChild::GetFrom(win);
    if (browserChild) {
      browserChild->SendShowCanvasPermissionPrompt(origin, isAutoBlockCanvas);
    }
  } else {
    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
    if (obs) {
      obs->NotifyObservers(win,
                           isAutoBlockCanvas
                               ? TOPIC_CANVAS_PERMISSIONS_PROMPT_HIDE_DOORHANGER
                               : TOPIC_CANVAS_PERMISSIONS_PROMPT,
                           NS_ConvertUTF8toUTF16(origin).get());
    }
  }

  // We don't extract the image for now -- user may override at prompt.
  return false;
}

bool GetCanvasContextType(const nsAString& str,
                          dom::CanvasContextType* const out_type) {
  if (str.EqualsLiteral("2d")) {
    *out_type = dom::CanvasContextType::Canvas2D;
    return true;
  }

  if (str.EqualsLiteral("webgl") || str.EqualsLiteral("experimental-webgl")) {
    *out_type = dom::CanvasContextType::WebGL1;
    return true;
  }

  if (StaticPrefs::webgl_enable_webgl2()) {
    if (str.EqualsLiteral("webgl2")) {
      *out_type = dom::CanvasContextType::WebGL2;
      return true;
    }
  }

  if (gfxVars::AllowWebGPU()) {
    if (str.EqualsLiteral("webgpu")) {
      *out_type = dom::CanvasContextType::WebGPU;
      return true;
    }
  }

  if (str.EqualsLiteral("bitmaprenderer")) {
    *out_type = dom::CanvasContextType::ImageBitmap;
    return true;
  }

  return false;
}

/**
 * This security check utility might be called from an source that never taints
 * others. For example, while painting a CanvasPattern, which is created from an
 * ImageBitmap, onto a canvas. In this case, the caller could set the CORSUsed
 * true in order to pass this check and leave the aPrincipal to be a nullptr
 * since the aPrincipal is not going to be used.
 */
void DoDrawImageSecurityCheck(dom::HTMLCanvasElement* aCanvasElement,
                              nsIPrincipal* aPrincipal, bool forceWriteOnly,
                              bool CORSUsed) {
  // Callers should ensure that mCanvasElement is non-null before calling this
  if (!aCanvasElement) {
    NS_WARNING("DoDrawImageSecurityCheck called without canvas element!");
    return;
  }

  if (aCanvasElement->IsWriteOnly() && !aCanvasElement->mExpandedReader) {
    return;
  }

  // If we explicitly set WriteOnly just do it and get out
  if (forceWriteOnly) {
    aCanvasElement->SetWriteOnly();
    return;
  }

  // No need to do a security check if the image used CORS for the load
  if (CORSUsed) return;

  MOZ_ASSERT(aPrincipal, "Must have a principal here");

  if (aCanvasElement->NodePrincipal()->Subsumes(aPrincipal)) {
    // This canvas has access to that image anyway
    return;
  }

  if (BasePrincipal::Cast(aPrincipal)->AddonPolicy()) {
    // This is a resource from an extension content script principal.

    if (aCanvasElement->mExpandedReader &&
        aCanvasElement->mExpandedReader->Subsumes(aPrincipal)) {
      // This canvas already allows reading from this principal.
      return;
    }

    if (!aCanvasElement->mExpandedReader) {
      // Allow future reads from this same princial only.
      aCanvasElement->SetWriteOnly(aPrincipal);
      return;
    }

    // If we got here, this must be the *second* extension tainting
    // the canvas.  Fall through to mark it WriteOnly for everyone.
  }

  aCanvasElement->SetWriteOnly();
}

bool CoerceDouble(const JS::Value& v, double* d) {
  if (v.isDouble()) {
    *d = v.toDouble();
  } else if (v.isInt32()) {
    *d = double(v.toInt32());
  } else if (v.isUndefined()) {
    *d = 0.0;
  } else {
    return false;
  }
  return true;
}

bool HasDrawWindowPrivilege(JSContext* aCx, JSObject* /* unused */) {
  return nsContentUtils::CallerHasPermission(aCx,
                                             nsGkAtoms::all_urlsPermission);
}

bool IsOffscreenCanvasEnabled(JSContext* aCx, JSObject* aObj) {
  if (StaticPrefs::gfx_offscreencanvas_enabled()) {
    return true;
  }

  if (OriginTrials::IsEnabled(aCx, aObj, OriginTrial::OffscreenCanvas)) {
    return true;
  }

  if (!StaticPrefs::gfx_offscreencanvas_domain_enabled()) {
    return false;
  }

  const auto& allowlist = gfxVars::GetOffscreenCanvasDomainAllowlistOrDefault();

  if (!NS_IsMainThread()) {
    dom::WorkerPrivate* workerPrivate = dom::GetWorkerPrivateFromContext(aCx);
    if (workerPrivate->UsesSystemPrincipal() ||
        workerPrivate->OriginNoSuffix() == u"resource://pdf.js"_ns) {
      return true;
    }

    return nsContentUtils::IsURIInList(workerPrivate->GetBaseURI(), allowlist);
  }

  nsIPrincipal* principal = nsContentUtils::SubjectPrincipal(aCx);
  if (principal->IsSystemPrincipal() || nsContentUtils::IsPDFJS(principal)) {
    return true;
  }

  nsCOMPtr<nsIURI> uri = principal->GetURI();
  return nsContentUtils::IsURIInList(uri, allowlist);
}

bool CheckWriteOnlySecurity(bool aCORSUsed, nsIPrincipal* aPrincipal,
                            bool aHadCrossOriginRedirects) {
  if (!aPrincipal) {
    return true;
  }

  if (!aCORSUsed) {
    if (aHadCrossOriginRedirects) {
      return true;
    }

    nsIGlobalObject* incumbentSettingsObject = dom::GetIncumbentGlobal();
    if (!incumbentSettingsObject) {
      return true;
    }

    nsIPrincipal* principal = incumbentSettingsObject->PrincipalOrNull();
    if (NS_WARN_IF(!principal) || !(principal->Subsumes(aPrincipal))) {
      return true;
    }
  }

  return false;
}

}  // namespace mozilla::CanvasUtils