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#include "proto.h"
#include "util.h"
#include <assert.h>
#include <stdlib.h>
enum {
Version = 0,
HdrLen = 0,
TotalLen = 2,
Id = 4,
FragInfo = 6,
EvilBit = 0x8000,
DontFrag = 0x4000,
MoreFrags = 0x2000,
FragOff = 0x1FFF,
TTL = 8,
Proto = 9,
Checksum = 10,
SrcIP = 12,
DstIP = 16,
};
static void ipv4_dispatch(const uint8_t *buf, size_t len, struct ipv4 ip);
struct fragment {
struct fragment *next; /* sorted */
size_t len, offset;
bool last;
uint8_t buf[];
};
struct fragmented {
/* src, dst, proto, id come from the first arrived packet
* and are used to tell fragmenteds apart.
* the rest comes from the sequentially first packet.
* ip.h.header points to a malloc'd buffer*/
struct ipv4 h;
struct fragment *first;
struct fragmented *next, **prev; /* *(inc->prev) == inc */
// TODO timer
};
struct fragmented *fragmenteds;
static struct fragmented *fragmented_find(struct ipv4 fraghdr);
static void fragmented_tryinsert(const uint8_t *payload, size_t plen, struct ipv4 ip);
static void fragmented_tryfinish(struct fragmented *inc);
static void fragmented_free(struct fragmented *inc);
static struct fragmented *fragmented_find(struct ipv4 fraghdr) {
struct fragmented *inc;
for (inc = fragmenteds; inc; inc = inc->next) {
if (inc->h.src == fraghdr.src &&
inc->h.dst == fraghdr.dst &&
inc->h.proto == fraghdr.proto &&
inc->h.id == fraghdr.id)
{
return inc;
}
}
inc = malloc(sizeof *inc);
memset(inc, 0, sizeof *inc);
inc->h.src = fraghdr.src;
inc->h.dst = fraghdr.dst;
inc->h.proto = fraghdr.proto;
inc->h.id = fraghdr.id;
inc->next = fragmenteds;
if (inc->next) inc->next->prev = &inc->next;
inc->prev = &fragmenteds;
*inc->prev = inc;
return inc;
}
static void fragmented_tryinsert(const uint8_t *payload, size_t plen, struct ipv4 ip) {
struct fragmented *inc = fragmented_find(ip);
size_t off = (ip.fraginfo & FragOff) * 8;
bool last = !(ip.fraginfo & MoreFrags);
// eprintf("fragmented packet, %u + %u, part of 0x%x", off, plen, inc);
/* find the first fragment at a bigger offset, and insert before it */
struct fragment **insert = &inc->first;
for (; *insert; insert = &(*insert)->next) {
if ((*insert)->offset > off) break;
if ((*insert)->offset == off) return; /* duplicate packet */
}
/* later on: frag->next = *insert;
* if we're the last fragment, frag->next must == NULL */
if (last && *insert != NULL) return;
struct fragment *frag = malloc(sizeof(struct fragment) + plen);
frag->next = *insert;
*insert = frag;
frag->len = plen;
frag->offset = off;
frag->last = last;
memcpy(frag->buf, payload, plen);
if (off == 0) { /* save header */
assert(!inc->h.header);
void *headercpy = malloc(ip.hlen);
memcpy(headercpy, ip.header, ip.hlen);
inc->h = ip;
inc->h.header = headercpy;
}
fragmented_tryfinish(inc);
}
static void fragmented_tryfinish(struct fragmented *inc) {
if (inc->first->offset != 0) return;
for (struct fragment *iter = inc->first; iter; iter = iter->next) {
size_t iterend = iter->offset + iter->len;
struct fragment *next = iter->next;
if (next) {
if (iterend < next->offset) return; /* incomplete */
if (iterend > next->offset) {
fragmented_free(inc);
return;
}
} else if (iter->last) {
void *buf = malloc(iterend);
for (struct fragment *iter = inc->first; iter; iter = iter->next) {
assert(iter->offset + iter->len <= iterend);
memcpy(buf + iter->offset, iter->buf, iter->len);
}
ipv4_dispatch(buf, iterend, inc->h);
free(buf);
fragmented_free(inc);
}
}
}
static void fragmented_free(struct fragmented *inc) {
if (inc->next) {
inc->next->prev = inc->prev;
*inc->next->prev = inc->next;
} else {
*inc->prev = NULL;
}
for (struct fragment *next, *iter = inc->first; iter; iter = next) {
next = iter->next;
free(iter);
}
free((void*)inc->h.header);
free(inc);
}
static void ipv4_dispatch(const uint8_t *buf, size_t len, struct ipv4 ip) {
switch (ip.proto) {
case 0x01: icmp_parse(buf, len, ip); break;
case 0x11: udp_parse(buf, len, ip); break;
}
}
void ipv4_parse(const uint8_t *buf, size_t len, struct ethernet ether) {
uint8_t version, headerlen;
uint16_t totallen;
version = buf[Version] >> 4;
if (version != 4) return;
headerlen = (buf[HdrLen] & 0xf) * 4;
totallen = nget16(buf + TotalLen);
if (totallen < headerlen) return;
/* ignores checksum. TODO? */
struct ipv4 ip = (struct ipv4){
.e = ether,
.src = nget32(buf + SrcIP),
.dst = nget32(buf + DstIP),
.id = nget16(buf + Id),
.fraginfo = nget16(buf + FragInfo),
.proto = buf[Proto],
.header = buf,
.hlen = headerlen,
};
if (ip.fraginfo & ~(EvilBit | DontFrag)) {
fragmented_tryinsert(buf + headerlen, totallen - headerlen, ip);
} else {
if (totallen > len) return;
ipv4_dispatch(buf + headerlen, totallen - headerlen, ip);
}
}
static uint16_t next_id = 0;
void ipv4_send(const void *payload, size_t len, struct ipv4 ip) {
const size_t mtu = 1500;
const size_t hdrlen = 20;
ip.e.type = ET_IPv4;
if (!ip.src) ip.src = state.ip;
if (!ip.e.dst && ip.dst == 0xFFFFFFFF)
ip.e.dst = &MAC_BROADCAST;
uint16_t id = next_id++;
for (size_t off = 0, fraglen = mtu - hdrlen; off < len; off += fraglen) {
if (fraglen > len - off)
fraglen = len - off;
bool last = off + fraglen >= len;
uint8_t *pkt = ether_start(hdrlen + fraglen, ip.e);
pkt[Version] = 0x40;
pkt[HdrLen] |= hdrlen / 4;
nput16(pkt + TotalLen, hdrlen + fraglen);
nput16(pkt + Id, id);
nput16(pkt + FragInfo, (off >> 3) | (last ? 0 : MoreFrags));
pkt[TTL] = 0xFF;
pkt[Proto] = ip.proto;
nput32(pkt + SrcIP, ip.src);
nput32(pkt + DstIP, ip.dst);
nput16(pkt + Checksum, ip_checksum(pkt, hdrlen));
memcpy(pkt + hdrlen, payload + off, fraglen);
ether_finish(pkt);
}
}
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