ed7b4602b5
Introduce the library libclat to implement clat functions for jni.
It is helpful for unit test.
makeChecksumNeutral() and its test are moved from ClatdController
without behavior change.
Bug: 212345928
Test: build and boot
atest libclat_test
Change-Id: I1c0981d98141fc1cc07b2d3a0f3cbddf38683ff3
52 lines
1.8 KiB
C++
52 lines
1.8 KiB
C++
// Copyright (C) 2022 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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#include "libclat/clatutils.h"
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#include <stdlib.h>
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extern "C" {
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#include "checksum.h"
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}
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namespace android {
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namespace net {
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namespace clat {
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// Alters the bits in the IPv6 address to make them checksum neutral with v4 and nat64Prefix.
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void makeChecksumNeutral(in6_addr* v6, const in_addr v4, const in6_addr& nat64Prefix) {
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// Fill last 8 bytes of IPv6 address with random bits.
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arc4random_buf(&v6->s6_addr[8], 8);
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// Make the IID checksum-neutral. That is, make it so that:
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// checksum(Local IPv4 | Remote IPv4) = checksum(Local IPv6 | Remote IPv6)
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// in other words (because remote IPv6 = NAT64 prefix | Remote IPv4):
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// checksum(Local IPv4) = checksum(Local IPv6 | NAT64 prefix)
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// Do this by adjusting the two bytes in the middle of the IID.
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uint16_t middlebytes = (v6->s6_addr[11] << 8) + v6->s6_addr[12];
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uint32_t c1 = ip_checksum_add(0, &v4, sizeof(v4));
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uint32_t c2 = ip_checksum_add(0, &nat64Prefix, sizeof(nat64Prefix)) +
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ip_checksum_add(0, v6, sizeof(*v6));
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uint16_t delta = ip_checksum_adjust(middlebytes, c1, c2);
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v6->s6_addr[11] = delta >> 8;
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v6->s6_addr[12] = delta & 0xff;
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}
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} // namespace clat
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} // namespace net
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} // namespace android
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