| // Copyright (C) 2022 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. |
| |
| #include "libclat/clatutils.h" |
| |
| #include <stdlib.h> |
| |
| extern "C" { |
| #include "checksum.h" |
| } |
| |
| namespace android { |
| namespace net { |
| namespace clat { |
| |
| // Alters the bits in the IPv6 address to make them checksum neutral with v4 and nat64Prefix. |
| void makeChecksumNeutral(in6_addr* v6, const in_addr v4, const in6_addr& nat64Prefix) { |
| // Fill last 8 bytes of IPv6 address with random bits. |
| arc4random_buf(&v6->s6_addr[8], 8); |
| |
| // Make the IID checksum-neutral. That is, make it so that: |
| // checksum(Local IPv4 | Remote IPv4) = checksum(Local IPv6 | Remote IPv6) |
| // in other words (because remote IPv6 = NAT64 prefix | Remote IPv4): |
| // checksum(Local IPv4) = checksum(Local IPv6 | NAT64 prefix) |
| // Do this by adjusting the two bytes in the middle of the IID. |
| |
| uint16_t middlebytes = (v6->s6_addr[11] << 8) + v6->s6_addr[12]; |
| |
| uint32_t c1 = ip_checksum_add(0, &v4, sizeof(v4)); |
| uint32_t c2 = ip_checksum_add(0, &nat64Prefix, sizeof(nat64Prefix)) + |
| ip_checksum_add(0, v6, sizeof(*v6)); |
| |
| uint16_t delta = ip_checksum_adjust(middlebytes, c1, c2); |
| v6->s6_addr[11] = delta >> 8; |
| v6->s6_addr[12] = delta & 0xff; |
| } |
| |
| } // namespace clat |
| } // namespace net |
| } // namespace android |