1/*
2 * Copyright 2011 Daniel Drown
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 * ipv4.c - takes ipv4 packets, finds their headers, and then calls translation functions on them
17 */
18#include <string.h>
19
20#include "translate.h"
21#include "checksum.h"
22#include "logging.h"
23#include "debug.h"
24#include "dump.h"
25
26/* function: icmp_packet
27 * translates an icmp packet
28 * out      - output packet
29 * icmp     - pointer to icmp header in packet
30 * checksum - pseudo-header checksum
31 * len      - size of ip payload
32 * returns: the highest position in the output clat_packet that's filled in
33 */
34int icmp_packet(clat_packet out, clat_packet_index pos, const struct icmphdr *icmp,
35                uint32_t checksum, size_t len) {
36  const uint8_t *payload;
37  size_t payload_size;
38
39  if(len < sizeof(struct icmphdr)) {
40    logmsg_dbg(ANDROID_LOG_ERROR, "icmp_packet/(too small)");
41    return 0;
42  }
43
44  payload = (const uint8_t *) (icmp + 1);
45  payload_size = len - sizeof(struct icmphdr);
46
47  return icmp_to_icmp6(out, pos, icmp, checksum, payload, payload_size);
48}
49
50/* function: ipv4_packet
51 * translates an ipv4 packet
52 * out    - output packet
53 * packet - packet data
54 * len    - size of packet
55 * returns: the highest position in the output clat_packet that's filled in
56 */
57int ipv4_packet(clat_packet out, clat_packet_index pos, const uint8_t *packet, size_t len) {
58  const struct iphdr *header = (struct iphdr *) packet;
59  struct ip6_hdr *ip6_targ = (struct ip6_hdr *) out[pos].iov_base;
60  struct ip6_frag *frag_hdr;
61  size_t frag_hdr_len;
62  uint8_t nxthdr;
63  const uint8_t *next_header;
64  size_t len_left;
65  uint32_t old_sum, new_sum;
66  int iov_len;
67
68  if(len < sizeof(struct iphdr)) {
69    logmsg_dbg(ANDROID_LOG_ERROR, "ip_packet/too short for an ip header");
70    return 0;
71  }
72
73  if(header->ihl < 5) {
74    logmsg_dbg(ANDROID_LOG_ERROR, "ip_packet/ip header length set to less than 5: %x", header->ihl);
75    return 0;
76  }
77
78  if((size_t) header->ihl * 4 > len) { // ip header length larger than entire packet
79    logmsg_dbg(ANDROID_LOG_ERROR, "ip_packet/ip header length set too large: %x", header->ihl);
80    return 0;
81  }
82
83  if(header->version != 4) {
84    logmsg_dbg(ANDROID_LOG_ERROR, "ip_packet/ip header version not 4: %x", header->version);
85    return 0;
86  }
87
88  /* rfc6145 - If any IPv4 options are present in the IPv4 packet, they MUST be
89   * ignored and the packet translated normally; there is no attempt to
90   * translate the options.
91   */
92
93  next_header = packet + header->ihl*4;
94  len_left = len - header->ihl * 4;
95
96  nxthdr = header->protocol;
97  if (nxthdr == IPPROTO_ICMP) {
98    // ICMP and ICMPv6 have different protocol numbers.
99    nxthdr = IPPROTO_ICMPV6;
100  }
101
102  /* Fill in the IPv6 header. We need to do this before we translate the packet because TCP and
103   * UDP include parts of the IP header in the checksum. Set the length to zero because we don't
104   * know it yet.
105   */
106  fill_ip6_header(ip6_targ, 0, nxthdr, header);
107  out[pos].iov_len = sizeof(struct ip6_hdr);
108
109  /* Calculate the pseudo-header checksum.
110   * Technically, the length that is used in the pseudo-header checksum is the transport layer
111   * length, which is not the same as len_left in the case of fragmented packets. But since
112   * translation does not change the transport layer length, the checksum is unaffected.
113   */
114  old_sum = ipv4_pseudo_header_checksum(header, len_left);
115  new_sum = ipv6_pseudo_header_checksum(ip6_targ, len_left, nxthdr);
116
117  // If the IPv4 packet is fragmented, add a Fragment header.
118  frag_hdr = (struct ip6_frag *) out[pos + 1].iov_base;
119  frag_hdr_len = maybe_fill_frag_header(frag_hdr, ip6_targ, header);
120  out[pos + 1].iov_len = frag_hdr_len;
121
122  if (frag_hdr_len && frag_hdr->ip6f_offlg & IP6F_OFF_MASK) {
123    // Non-first fragment. Copy the rest of the packet as is.
124    iov_len = generic_packet(out, pos + 2, next_header, len_left);
125  } else if (nxthdr == IPPROTO_ICMPV6) {
126    iov_len = icmp_packet(out, pos + 2, (const struct icmphdr *) next_header, new_sum, len_left);
127  } else if (nxthdr == IPPROTO_TCP) {
128    iov_len = tcp_packet(out, pos + 2, (const struct tcphdr *) next_header, old_sum, new_sum,
129                         len_left);
130  } else if (nxthdr == IPPROTO_UDP) {
131    iov_len = udp_packet(out, pos + 2, (const struct udphdr *) next_header, old_sum, new_sum,
132                         len_left);
133  } else if (nxthdr == IPPROTO_GRE) {
134    iov_len = generic_packet(out, pos + 2, next_header, len_left);
135  } else {
136#if CLAT_DEBUG
137    logmsg_dbg(ANDROID_LOG_ERROR, "ip_packet/unknown protocol: %x",header->protocol);
138    logcat_hexdump("ipv4/protocol", packet, len);
139#endif
140    return 0;
141  }
142
143  // Set the length.
144  ip6_targ->ip6_plen = htons(packet_length(out, pos));
145  return iov_len;
146}
147