//
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// Copyright (C) 2014 The Android Open Source Project
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//
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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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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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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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#include "update_engine/update_manager/real_random_provider.h"
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#include <stdio.h>
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#include <unistd.h>
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#include <string>
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#include <base/files/file_path.h>
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#include <base/files/scoped_file.h>
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#include <base/strings/stringprintf.h>
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#include "update_engine/update_manager/variable.h"
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using std::string;
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namespace {
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// The device providing randomness.
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const char* kRandomDevice = "/dev/urandom";
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} // namespace
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namespace chromeos_update_manager {
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// A random seed variable.
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class RandomSeedVariable : public Variable<uint64_t> {
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public:
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// RandomSeedVariable is initialized as kVariableModeConst to let the
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// EvaluationContext cache the value between different evaluations of the same
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// policy request.
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RandomSeedVariable(const string& name, FILE* fp)
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: Variable<uint64_t>(name, kVariableModeConst), fp_(fp) {}
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~RandomSeedVariable() override {}
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protected:
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const uint64_t* GetValue(base::TimeDelta /* timeout */,
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string* errmsg) override {
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uint64_t result;
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// Aliasing via char pointer abides by the C/C++ strict-aliasing rules.
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char* const buf = reinterpret_cast<char*>(&result);
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unsigned int buf_rd = 0;
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while (buf_rd < sizeof(result)) {
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int rd = fread(buf + buf_rd, 1, sizeof(result) - buf_rd, fp_.get());
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if (rd == 0 || ferror(fp_.get())) {
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// Either EOF on fp or read failed.
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if (errmsg) {
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*errmsg = base::StringPrintf(
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"Error reading from the random device: %s", kRandomDevice);
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}
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return nullptr;
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}
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buf_rd += rd;
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}
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return new uint64_t(result);
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}
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private:
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base::ScopedFILE fp_;
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DISALLOW_COPY_AND_ASSIGN(RandomSeedVariable);
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};
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bool RealRandomProvider::Init(void) {
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FILE* fp = fopen(kRandomDevice, "r");
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if (!fp)
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return false;
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var_seed_.reset(new RandomSeedVariable("seed", fp));
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return true;
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}
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} // namespace chromeos_update_manager
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