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packet.c
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packet.c
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/*
* Copyright 2013 Google Inc.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*/
/*
* Author: ncardwell@google.com (Neal Cardwell)
*
* Implementation for a representation of TCP/IP packets.
* Packets are represented in their wire format.
*/
#include "packet.h"
#include <stdlib.h>
#include <string.h>
#include "assert.h"
#include "ethernet.h"
#include "gre_packet.h"
#include "ip_packet.h"
#include "logging.h"
#include "mpls_packet.h"
/* Info for all types of header we support. */
struct header_type_info header_types[HEADER_NUM_TYPES] = {
{ "NONE", 0, 0, NULL },
{ "IPV4", IPPROTO_IPIP, ETHERTYPE_IP, ipv4_header_finish },
{ "IPV6", IPPROTO_IPV6, ETHERTYPE_IPV6, ipv6_header_finish },
{ "GRE", IPPROTO_GRE, 0, gre_header_finish },
{ "MPLS", 0, ETHERTYPE_MPLS_UC, mpls_header_finish },
{ "TCP", IPPROTO_TCP, 0, NULL },
{ "UDP", IPPROTO_UDP, 0, NULL },
{ "ICMPV4", IPPROTO_ICMP, 0, NULL },
{ "ICMPV6", IPPROTO_ICMPV6, 0, NULL },
};
struct packet *packet_new(u32 buffer_bytes)
{
struct packet *packet = calloc(1, sizeof(struct packet));
packet->buffer = malloc(buffer_bytes);
packet->buffer_bytes = buffer_bytes;
return packet;
}
void packet_free(struct packet *packet)
{
free(packet->buffer);
memset(packet, 0, sizeof(*packet)); /* paranoia to help catch bugs */
free(packet);
}
struct packet_list *packet_list_new(void)
{
struct packet_list *list = calloc(1, sizeof(struct packet_list));
list->packet = NULL;
list->next = NULL;
return list;
}
void packet_list_free(struct packet_list *list)
{
while (list != NULL) {
struct packet_list *dead_list = list;
if (list->packet)
packet_free(list->packet);
list = list->next;
free(dead_list);
}
}
int packet_header_count(const struct packet *packet)
{
int i;
for (i = 0; i < ARRAY_SIZE(packet->headers); ++i) {
if (packet->headers[i].type == HEADER_NONE)
break;
}
return i;
}
/* Copy any header info from old_packet to new_packet. */
static void packet_copy_headers(struct packet *new_packet,
struct packet *old_packet,
int bytes_headroom)
{
int i;
u8 *base = new_packet->buffer + bytes_headroom;
for (i = 0; i < ARRAY_SIZE(old_packet->headers); ++i) {
struct header *old_header = &old_packet->headers[i];
struct header *new_header = &new_packet->headers[i];
int offset = 0;
if (old_header->type == HEADER_NONE)
break;
offset = old_header->h.ptr - old_packet->buffer;
new_header->h.ptr = base + offset;
new_header->header_bytes = old_header->header_bytes;
new_header->total_bytes = old_header->total_bytes;
new_header->type = old_header->type;
}
}
struct header *packet_append_header(struct packet *packet,
enum header_t header_type,
int header_bytes)
{
struct header *header = NULL;
int num_headers = packet_header_count(packet);
int packet_bytes;
assert(num_headers <= PACKET_MAX_HEADERS);
if (num_headers == PACKET_MAX_HEADERS)
return NULL;
header = &packet->headers[num_headers];
if (packet->ip_bytes + header_bytes > packet->buffer_bytes)
return NULL;
packet_bytes = packet->l2_header_bytes + packet->ip_bytes;
header->h.ptr = packet->buffer + packet_bytes;
packet->ip_bytes += header_bytes;
header->type = header_type;
header->header_bytes = header_bytes;
header->total_bytes = 0;
return header;
}
/* Map a pointer to a packet offset from an old base to a new base. */
static void *offset_ptr(u8 *old_base, u8* new_base, void *old_ptr)
{
u8 *old = (u8*)old_ptr;
return (old == NULL) ? NULL : (new_base + (old - old_base));
}
static void packet_duplicate_info(struct packet *packet,
struct packet *old_packet,
int bytes_headroom,
int extra_payload)
{
u8 *old_base = old_packet->buffer;
u8 *new_base = packet->buffer + bytes_headroom;
packet->ip_bytes = old_packet->ip_bytes + extra_payload;
packet->direction = old_packet->direction;
packet->time_usecs = old_packet->time_usecs;
packet->flags = old_packet->flags;
packet->tos_chk = old_packet->tos_chk;
packet_copy_headers(packet, old_packet, bytes_headroom);
/* Set up layer 3 header pointer. */
packet->ipv4 = offset_ptr(old_base, new_base, old_packet->ipv4);
packet->ipv6 = offset_ptr(old_base, new_base, old_packet->ipv6);
packet->tcp = offset_ptr(old_base, new_base, old_packet->tcp);
packet->udp = offset_ptr(old_base, new_base, old_packet->udp);
packet->icmpv4 = offset_ptr(old_base, new_base, old_packet->icmpv4);
packet->icmpv6 = offset_ptr(old_base, new_base, old_packet->icmpv6);
packet->tcp_ts_val = offset_ptr(old_base, new_base,
old_packet->tcp_ts_val);
packet->tcp_ts_ecr = offset_ptr(old_base, new_base,
old_packet->tcp_ts_ecr);
packet->echoed_header = old_packet->echoed_header;
}
/* Make a copy of the given old packet, but in the new copy reserve the
* given number of bytes of headroom at the start of the packet->buffer.
* This empty headroom can later be filled with outer packet headers.
* A slow but simple model.
*/
static struct packet *packet_copy_with_headroom(struct packet *old_packet,
int bytes_headroom)
{
/* Allocate a new packet and copy link layer header and IP datagram. */
const int bytes_used = packet_end(old_packet) - old_packet->buffer;
assert(bytes_used >= 0);
assert(bytes_used <= 128*1024);
struct packet *packet = packet_new(bytes_headroom + bytes_used);
u8 *old_base = old_packet->buffer;
u8 *new_base = packet->buffer + bytes_headroom;
memcpy(new_base, old_base, bytes_used);
packet_duplicate_info(packet, old_packet, bytes_headroom, 0);
return packet;
}
struct packet *packet_copy(struct packet *old_packet)
{
return packet_copy_with_headroom(old_packet, 0);
}
/* Finalize all the headers once we know what's inside inner layers. */
static void packet_finish_encapsulation_headers(struct packet *packet)
{
int i;
struct header *header = NULL, *next = NULL;
/* Proceed from inner to outer. */
for (i = ARRAY_SIZE(packet->headers) - 1; i >= 0; --i, next = header) {
struct header_type_info *type_info = NULL;
header = &packet->headers[i];
if (header->type == HEADER_NONE)
continue;
type_info = header_type_info(header->type);
if (type_info->finish != NULL)
type_info->finish(packet, header, next);
}
}
struct packet *packet_encapsulate(struct packet *outer, struct packet *inner)
{
struct packet *packet = NULL;
const int outer_headers = packet_header_count(outer);
const int inner_headers = packet_header_count(inner);
assert(outer_headers + inner_headers <= PACKET_MAX_HEADERS);
/* Copy the inner packet bits and header metadata. */
packet = packet_copy_with_headroom(inner, outer->ip_bytes);
/* Copy over the bits in the outer headers. */
memcpy(packet->buffer, outer->buffer, outer->ip_bytes);
/* Move the inner header metadata to make room for the outer. */
memmove(packet->headers + outer_headers, packet->headers + 0,
inner_headers * sizeof(struct header));
/* Copy over the metadata about the outer headers. */
packet_copy_headers(packet, outer, 0);
assert(packet_header_count(packet) == outer_headers + inner_headers);
packet_finish_encapsulation_headers(packet);
packet->ip_bytes = outer->ip_bytes + inner->ip_bytes;
return packet;
}
struct header_type_info *header_type_info(enum header_t header_type)
{
assert(header_type > HEADER_NONE);
assert(header_type < HEADER_NUM_TYPES);
assert(ARRAY_SIZE(header_types) == HEADER_NUM_TYPES);
return &header_types[header_type];
}
/* Aggregate a list of input packets into a single output packet. */
struct packet *aggregate_packets(const struct packet_list *head,
const struct packet_list *tail,
int payload_size)
{
int i;
/* Copy the headers from the last source packet. */
struct packet *first_packet = head->packet;
struct packet *last_packet = tail->packet;
struct packet *old_packet = last_packet;
/* Allocate a new packet that can accommodate the combined payload */
int extra_payload = payload_size - packet_payload_len(old_packet);
int headers_len = packet_payload(old_packet) - old_packet->buffer;
int old_packet_size = packet_end(old_packet) - old_packet->buffer;
struct packet *packet = packet_new(old_packet_size + extra_payload);
u8 *old_base = old_packet->buffer;
u8 *new_base = packet->buffer;
u8 *iter_base = new_base + headers_len;
DEBUGP("aggregate_packets with combined payload size of %d bytes\n",
payload_size);
memcpy(new_base, old_base, headers_len);
/* Copy the payload from all the source packets. */
do {
memcpy(iter_base, packet_payload(head->packet),
packet_payload_len(head->packet));
iter_base += packet_payload_len(head->packet);
head = head->next;
} while (head != NULL);
packet_duplicate_info(packet, old_packet, 0, extra_payload);
/* Adjust header bytes information to account for the larger payload. */
for (i = 0; i < ARRAY_SIZE(packet->headers); ++i) {
struct header *new_header = &packet->headers[i];
if (new_header->type == HEADER_NONE)
break;
new_header->total_bytes += extra_payload;
DEBUGP("%s header starts at %p\n",
header_type_info(new_header->type)->name,
new_header->h.ptr);
/* For TCP header, we must copy the seq number and the cwr flag
* from the first packet.
*/
if (new_header->type == HEADER_TCP) {
assert(packet->tcp != NULL);
assert(first_packet->tcp != NULL);
packet->tcp->seq = first_packet->tcp->seq;
packet->tcp->cwr = first_packet->tcp->cwr;
}
}
packet_finish_encapsulation_headers(packet);
return packet;
}