зеркало из https://github.com/mozilla/gecko-dev.git
98 строки
3.4 KiB
C++
98 строки
3.4 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_dom_GeneratePlaceholderCanvasData_h
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#define mozilla_dom_GeneratePlaceholderCanvasData_h
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#include "mozilla/StaticPrefs_privacy.h"
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#include "nsCOMPtr.h"
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#include "nsIRandomGenerator.h"
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#include "nsServiceManagerUtils.h"
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#define RANDOM_BYTES_TO_SAMPLE 32
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namespace mozilla::dom {
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/**
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* When privacy.resistFingerprinting.randomDataOnCanvasExtract is true, tries
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* to generate random data for placeholder canvas by sampling
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* RANDOM_BYTES_TO_SAMPLE bytes and then returning it. If this fails or if
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* privacy.resistFingerprinting.randomDataOnCanvasExtract is false, returns
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* nullptr.
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*
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* @return uint8_t* output buffer
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*/
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inline uint8_t* TryToGenerateRandomDataForPlaceholderCanvasData() {
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if (!StaticPrefs::privacy_resistFingerprinting_randomDataOnCanvasExtract()) {
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return nullptr;
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}
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nsresult rv;
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nsCOMPtr<nsIRandomGenerator> rg =
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do_GetService("@mozilla.org/security/random-generator;1", &rv);
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if (NS_FAILED(rv)) {
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return nullptr;
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}
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uint8_t* randomData;
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rv = rg->GenerateRandomBytes(RANDOM_BYTES_TO_SAMPLE, &randomData);
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if (NS_FAILED(rv)) {
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return nullptr;
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}
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return randomData;
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}
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/**
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* If randomData not nullptr, repeats those bytes many times to fill buffer. If
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* randomData is nullptr, returns all-white pixel data.
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*
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* @param[in] randomData Buffer of RANDOM_BYTES_TO_SAMPLE bytes of random
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* data, or nullptr
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* @param[in] size Size of output buffer
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* @param[out] buffer Output buffer
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*/
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inline void FillPlaceholderCanvas(uint8_t* randomData, uint32_t size,
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uint8_t* buffer) {
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if (!randomData) {
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memset(buffer, 0xFF, size);
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return;
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}
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auto remaining_to_fill = size;
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auto index = 0;
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while (remaining_to_fill > 0) {
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auto bytes_to_write = (remaining_to_fill > RANDOM_BYTES_TO_SAMPLE)
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? RANDOM_BYTES_TO_SAMPLE
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: remaining_to_fill;
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memcpy(buffer + (index * RANDOM_BYTES_TO_SAMPLE), randomData,
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bytes_to_write);
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remaining_to_fill -= bytes_to_write;
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index++;
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}
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free(randomData);
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}
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/**
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* When privacy.resistFingerprinting.randomDataOnCanvasExtract is true, tries
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* to generate random canvas data by sampling RANDOM_BYTES_TO_SAMPLE bytes and
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* then repeating those bytes many times to fill the buffer. If this fails or
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* if privacy.resistFingerprinting.randomDataOnCanvasExtract is false, returns
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* all-white, opaque pixel data.
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*
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* It is recommended that callers call this function instead of individually
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* calling TryToGenerateRandomDataForPlaceholderCanvasData and
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* FillPlaceholderCanvas unless there are requirements, like NoGC, that prevent
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* them from calling the RNG service inside this function.
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*
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* @param[in] size Size of output buffer
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* @param[out] buffer Output buffer
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*/
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inline void GeneratePlaceholderCanvasData(uint32_t size, uint8_t* buffer) {
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uint8_t* randomData = TryToGenerateRandomDataForPlaceholderCanvasData();
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FillPlaceholderCanvas(randomData, size, buffer);
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}
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} // namespace mozilla::dom
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#endif // mozilla_dom_GeneratePlaceholderCanvasData_h
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