cmds/incidentd/src/PrivacyBuffer.cpp

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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.
 */
#define DEBUG false
#include "Log.h"

#include "PrivacyBuffer.h"
#include "incidentd_util.h"

#include <android-base/file.h>
#include <android/util/protobuf.h>
#include <cutils/log.h>

using namespace android::util;

/**
 * Write the field to buf based on the wire type, iterator will point to next field.
 * If skip is set to true, no data will be written to buf. Return number of bytes written.
 */
void PrivacyBuffer::writeFieldOrSkip(uint32_t fieldTag, bool skip) {
    uint8_t wireType = read_wire_type(fieldTag);
    size_t bytesToWrite = 0;
    uint32_t varint = 0;

    switch (wireType) {
        case WIRE_TYPE_VARINT:
            varint = mData.readRawVarint();
            if (!skip) {
                mProto.writeRawVarint(fieldTag);
                mProto.writeRawVarint(varint);
            }
            return;
        case WIRE_TYPE_FIXED64:
            if (!skip) mProto.writeRawVarint(fieldTag);
            bytesToWrite = 8;
            break;
        case WIRE_TYPE_LENGTH_DELIMITED:
            bytesToWrite = mData.readRawVarint();
            if (!skip) mProto.writeLengthDelimitedHeader(read_field_id(fieldTag), bytesToWrite);
            break;
        case WIRE_TYPE_FIXED32:
            if (!skip) mProto.writeRawVarint(fieldTag);
            bytesToWrite = 4;
            break;
    }
    if (skip) {
        mData.rp()->move(bytesToWrite);
    } else {
        for (size_t i = 0; i < bytesToWrite; i++) {
            mProto.writeRawByte(mData.next());
        }
    }
}

/**
 * Strip next field based on its private policy and request spec, then stores data in buf.
 * Return NO_ERROR if succeeds, otherwise BAD_VALUE is returned to indicate bad data in FdBuffer.
 *
 * The iterator must point to the head of a protobuf formatted field for successful operation.
 * After exit with NO_ERROR, iterator points to the next protobuf field's head.
 */
status_t PrivacyBuffer::stripField(const Privacy* parentPolicy, const PrivacySpec& spec,
                                   int depth /* use as a counter for this recusive method. */) {
    if (!mData.hasNext() || parentPolicy == NULL) return BAD_VALUE;
    uint32_t fieldTag = mData.readRawVarint();
    uint32_t fieldId = read_field_id(fieldTag);
    const Privacy* policy = lookup(parentPolicy, fieldId);

    VLOG("[Depth %2d]Try to strip id %d, wiretype %d", depth, fieldId, read_wire_type(fieldTag));
    if (policy == NULL || policy->children == NULL) {
        bool skip = !spec.CheckPremission(policy, parentPolicy->dest);
        // iterator will point to head of next field
        size_t currentAt = mData.rp()->pos();
        writeFieldOrSkip(fieldTag, skip);
        VLOG("[Depth %2d]Field %d %ss %d bytes", depth, fieldId, skip ? "skip" : "write",
             (int)(get_varint_size(fieldTag) + mData.rp()->pos() - currentAt));
        return NO_ERROR;
    }
    // current field is message type and its sub-fields have extra privacy policies
    uint32_t msgSize = mData.readRawVarint();
    size_t start = mData.rp()->pos();
    uint64_t token = mProto.start(encode_field_id(policy));
    while (mData.rp()->pos() - start != msgSize) {
        status_t err = stripField(policy, spec, depth + 1);
        if (err != NO_ERROR) return err;
    }
    mProto.end(token);
    return NO_ERROR;
}

// ================================================================================
PrivacyBuffer::PrivacyBuffer(const Privacy* policy, EncodedBuffer::iterator& data)
    : mPolicy(policy), mData(data), mProto(), mSize(0) {}

PrivacyBuffer::~PrivacyBuffer() {}

status_t PrivacyBuffer::strip(const PrivacySpec& spec) {
    VLOG("Strip with spec %d", spec.dest);
    // optimization when no strip happens
    if (mPolicy == NULL || mPolicy->children == NULL || spec.RequireAll()) {
        if (spec.CheckPremission(mPolicy)) mSize = mData.size();
        return NO_ERROR;
    }
    while (mData.hasNext()) {
        status_t err = stripField(mPolicy, spec, 0);
        if (err != NO_ERROR) return err;
    }
    if (mData.bytesRead() != mData.size()) return BAD_VALUE;
    mSize = mProto.size();
    mData.rp()->rewind();  // rewind the read pointer back to beginning after the strip.
    return NO_ERROR;
}

void PrivacyBuffer::clear() {
    mSize = 0;
    mProto.clear();
}

size_t PrivacyBuffer::size() const { return mSize; }

status_t PrivacyBuffer::flush(int fd) {
    status_t err = NO_ERROR;
    EncodedBuffer::iterator iter = size() == mData.size() ? mData : mProto.data();
    while (iter.readBuffer() != NULL) {
        err = WriteFully(fd, iter.readBuffer(), iter.currentToRead()) ? NO_ERROR : -errno;
        iter.rp()->move(iter.currentToRead());
        if (err != NO_ERROR) return err;
    }
    return NO_ERROR;
}