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115 lines
4.8 KiB
JavaScript
115 lines
4.8 KiB
JavaScript
/*
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Copyright 2016 OpenMarket Ltd
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Copyright 2018 New Vector Ltd
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Pull in the encryption lib so that we can decrypt attachments.
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import encrypt from 'browser-encrypt-attachment';
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// Pull in a fetch polyfill so we can download encrypted attachments.
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import 'isomorphic-fetch';
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// Grab the client so that we can turn mxc:// URLs into https:// URLS.
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import MatrixClientPeg from '../MatrixClientPeg';
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import Promise from 'bluebird';
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// WARNING: We have to be very careful about what mime-types we allow into blobs,
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// as for performance reasons these are now rendered via URL.createObjectURL()
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// rather than by converting into data: URIs.
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//
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// This means that the content is rendered using the origin of the script which
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// called createObjectURL(), and so if the content contains any scripting then it
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// will pose a XSS vulnerability when the browser renders it. This is particularly
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// bad if the user right-clicks the URI and pastes it into a new window or tab,
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// as the blob will then execute with access to Riot's full JS environment(!)
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//
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// See https://github.com/matrix-org/matrix-react-sdk/pull/1820#issuecomment-385210647
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// for details.
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//
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// We mitigate this by only allowing mime-types into blobs which we know don't
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// contain any scripting, and instantiate all others as application/octet-stream
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// regardless of what mime-type the event claimed. Even if the payload itself
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// is some malicious HTML, the fact we instantiate it with a media mimetype or
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// application/octet-stream means the browser doesn't try to render it as such.
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//
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// One interesting edge case is image/svg+xml, which empirically *is* rendered
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// correctly if the blob is set to the src attribute of an img tag (for thumbnails)
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// *even if the mimetype is application/octet-stream*. However, empirically JS
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// in the SVG isn't executed in this scenario, so we seem to be okay.
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//
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// Tested on Chrome 65 and Firefox 60
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//
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// The list below is taken mainly from
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// https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats
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// N.B. Matrix doesn't currently specify which mimetypes are valid in given
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// events, so we pick the ones which HTML5 browsers should be able to display
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//
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// For the record, mime-types which must NEVER enter this list below include:
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// text/html, text/xhtml, image/svg, image/svg+xml, image/pdf, and similar.
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const ALLOWED_BLOB_MIMETYPES = {
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'image/jpeg': true,
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'image/gif': true,
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'image/png': true,
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'video/mp4': true,
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'video/webm': true,
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'video/ogg': true,
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'audio/mp4': true,
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'audio/webm': true,
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'audio/aac': true,
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'audio/mpeg': true,
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'audio/ogg': true,
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'audio/wave': true,
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'audio/wav': true,
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'audio/x-wav': true,
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'audio/x-pn-wav': true,
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'audio/flac': true,
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'audio/x-flac': true,
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};
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/**
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* Decrypt a file attached to a matrix event.
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* @param file {Object} The json taken from the matrix event.
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* This passed to [link]{@link https://github.com/matrix-org/browser-encrypt-attachments}
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* as the encryption info object, so will also have the those keys in addition to
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* the keys below.
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* @param file.url {string} An mxc:// URL for the encrypted file.
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* @param file.mimetype {string} The MIME-type of the plaintext file.
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*/
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export function decryptFile(file) {
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const url = MatrixClientPeg.get().mxcUrlToHttp(file.url);
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// Download the encrypted file as an array buffer.
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return Promise.resolve(fetch(url)).then(function(response) {
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return response.arrayBuffer();
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}).then(function(responseData) {
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// Decrypt the array buffer using the information taken from
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// the event content.
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return encrypt.decryptAttachment(responseData, file);
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}).then(function(dataArray) {
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// Turn the array into a Blob and give it the correct MIME-type.
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// IMPORTANT: we must not allow scriptable mime-types into Blobs otherwise
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// they introduce XSS attacks if the Blob URI is viewed directly in the
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// browser (e.g. by copying the URI into a new tab or window.)
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// See warning at top of file.
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let mimetype = file.mimetype ? file.mimetype.split(";")[0].trim() : '';
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if (!ALLOWED_BLOB_MIMETYPES[mimetype]) {
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mimetype = 'application/octet-stream';
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}
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const blob = new Blob([dataArray], {type: mimetype});
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return blob;
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});
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}
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