tor-browser

PsshParser.cpp (4999B)

---

/*
* Copyright 2015, Mozilla Foundation and contributors
*
* 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.
*/

#include "PsshParser.h"

#include <assert.h>
#include <memory.h>

#include <algorithm>
#include <limits>
#include <utility>

#include "mozilla/Assertions.h"
#include "mozilla/EndianUtils.h"

// Stripped down version of mp4_demuxer::ByteReader, stripped down to make it
// easier to link into ClearKey DLL and gtest.
class ByteReader {
public:
 ByteReader(const uint8_t* aData, size_t aSize)
     : mPtr(aData), mRemaining(aSize), mLength(aSize) {}

 size_t Offset() const { return mLength - mRemaining; }

 size_t Remaining() const { return mRemaining; }

 size_t Length() const { return mLength; }

 bool CanRead8() const { return mRemaining >= 1; }

 uint8_t ReadU8() {
   auto ptr = Read(1);
   if (!ptr) {
     MOZ_ASSERT(false);
     return 0;
   }
   return *ptr;
 }

 bool CanRead32() const { return mRemaining >= 4; }

 uint32_t ReadU32() {
   auto ptr = Read(4);
   if (!ptr) {
     MOZ_ASSERT(false);
     return 0;
   }
   return mozilla::BigEndian::readUint32(ptr);
 }

 const uint8_t* Read(size_t aCount) {
   if (aCount > mRemaining) {
     mRemaining = 0;
     return nullptr;
   }
   mRemaining -= aCount;

   const uint8_t* result = mPtr;
   mPtr += aCount;

   return result;
 }

 const uint8_t* Seek(size_t aOffset) {
   if (aOffset > mLength) {
     MOZ_ASSERT(false);
     return nullptr;
   }

   mPtr = mPtr - Offset() + aOffset;
   mRemaining = mLength - aOffset;
   return mPtr;
 }

private:
 const uint8_t* mPtr;
 size_t mRemaining;
 const size_t mLength;
};

#define FOURCC(a, b, c, d) ((a << 24) + (b << 16) + (c << 8) + d)

// System ID identifying the cenc v2 pssh box format; specified at:
// https://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-media/cenc-format.html
const uint8_t kSystemID[] = {0x10, 0x77, 0xef, 0xec, 0xc0, 0xb2, 0x4d, 0x02,
                            0xac, 0xe3, 0x3c, 0x1e, 0x52, 0xe2, 0xfb, 0x4b};

bool ParseCENCInitData(const uint8_t* aInitData, uint32_t aInitDataSize,
                      std::vector<std::vector<uint8_t>>& aOutKeyIds) {
 aOutKeyIds.clear();
 std::vector<std::vector<uint8_t>> keyIds;
 ByteReader reader(aInitData, aInitDataSize);
 while (reader.CanRead32()) {
   // Box size. For the common system Id, ignore this, as some useragents
   // handle invalid box sizes.
   const size_t start = reader.Offset();
   const size_t size = reader.ReadU32();
   if (size > std::numeric_limits<size_t>::max() - start) {
     // Ensure 'start + size' calculation below can't overflow.
     return false;
   }
   const size_t end = start + size;
   if (end > reader.Length()) {
     // Ridiculous sized box.
     return false;
   }

   // PSSH box type.
   if (!reader.CanRead32()) {
     return false;
   }
   uint32_t box = reader.ReadU32();
   if (box != FOURCC('p', 's', 's', 'h')) {
     return false;
   }

   // 1 byte version, 3 bytes flags.
   if (!reader.CanRead32()) {
     return false;
   }
   uint8_t version = reader.ReadU8();
   if (version != 1) {
     // Ignore pssh boxes with wrong version.
     reader.Seek(std::max<size_t>(reader.Offset(), end));
     continue;
   }
   reader.Read(3);  // skip flags.

   // SystemID
   const uint8_t* sid = reader.Read(sizeof(kSystemID));
   if (!sid) {
     // Insufficient bytes to read SystemID.
     return false;
   }

   if (memcmp(kSystemID, sid, sizeof(kSystemID))) {
     // Ignore pssh boxes with wrong system ID.
     reader.Seek(std::max<size_t>(reader.Offset(), end));
     continue;
   }

   if (!reader.CanRead32()) {
     return false;
   }
   uint32_t kidCount = reader.ReadU32();

   if (kidCount * CENC_KEY_LEN > reader.Remaining()) {
     // Not enough bytes remaining to read all keys.
     return false;
   }

   for (uint32_t i = 0; i < kidCount; i++) {
     const uint8_t* kid = reader.Read(CENC_KEY_LEN);
     keyIds.push_back(std::vector<uint8_t>(kid, kid + CENC_KEY_LEN));
   }

   // Size of extra data. EME CENC format spec says datasize should
   // always be 0. We explicitly read the datasize, in case the box
   // size was 0, so that we get to the end of the box.
   if (!reader.CanRead32()) {
     return false;
   }
   reader.ReadU32();

   // Jump forwards to the end of the box, skipping any padding.
   if (size) {
     reader.Seek(end);
   }
 }
 aOutKeyIds = std::move(keyIds);
 return true;
}