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- /*
- * mod_ip_frag.c
- *
- * Copyright (c) 2001 Dug Song <dugsong@monkey.org>
- *
- * $Id: mod_ip_frag.c 2000 2008-04-27 06:17:35Z aturner $
- */
- #include "config.h"
- #include <err.h>
- #include <stdio.h>
- #include <stdlib.h>
- #include <string.h>
- #include "mod.h"
- #include "pkt.h"
- #include "randutil.h"
- #ifndef MAX
- #define MAX(a,b) (((a)>(b))?(a):(b))
- #endif
- #define FAVOR_OLD 1
- #define FAVOR_NEW 2
- static struct ip_frag_data {
- rand_t *rnd;
- int size;
- int overlap;
- } ip_frag_data;
- void *
- ip_frag_close(void *d)
- {
- if (ip_frag_data.rnd != NULL)
- rand_close(ip_frag_data.rnd);
- ip_frag_data.size = 0;
- return (NULL);
- }
- void *
- ip_frag_open(int argc, char *argv[])
- {
- if (argc < 2) {
- warnx("need fragment <size> in bytes");
- return (NULL);
- }
- ip_frag_data.rnd = rand_open();
- ip_frag_data.size = atoi(argv[1]);
-
- if (ip_frag_data.size == 0 || (ip_frag_data.size % 8) != 0) {
- warnx("fragment size must be a multiple of 8");
- return (ip_frag_close(&ip_frag_data));
- }
- if (argc == 3) {
- if (strcmp(argv[2], "old") == 0 ||
- strcmp(argv[2], "win32") == 0)
- ip_frag_data.overlap = FAVOR_OLD;
- else if (strcmp(argv[2], "new") == 0 ||
- strcmp(argv[2], "unix") == 0)
- ip_frag_data.overlap = FAVOR_NEW;
- else
- return (ip_frag_close(&ip_frag_data));
- }
- return (&ip_frag_data);
- }
- int
- ip_frag_apply(void *d, struct pktq *pktq)
- {
- struct pkt *pkt, *new, *next, tmp;
- int hl, fraglen, off;
- u_char *p, *p1, *p2;
- for (pkt = TAILQ_FIRST(pktq); pkt != TAILQ_END(pktq); pkt = next) {
- next = TAILQ_NEXT(pkt, pkt_next);
-
- if (pkt->pkt_ip == NULL || pkt->pkt_ip_data == NULL)
- continue;
-
- hl = pkt->pkt_ip->ip_hl << 2;
-
- /*
- * Preserve transport protocol header in first frag,
- * to bypass filters that block `short' fragments.
- */
- switch (pkt->pkt_ip->ip_p) {
- case IP_PROTO_ICMP:
- fraglen = MAX(ICMP_LEN_MIN, ip_frag_data.size);
- break;
- case IP_PROTO_UDP:
- fraglen = MAX(UDP_HDR_LEN, ip_frag_data.size);
- break;
- case IP_PROTO_TCP:
- fraglen = MAX(pkt->pkt_tcp->th_off << 2,
- ip_frag_data.size);
- break;
- default:
- fraglen = ip_frag_data.size;
- break;
- }
- if (fraglen & 7)
- fraglen = (fraglen & ~7) + 8;
-
- if (pkt->pkt_end - pkt->pkt_ip_data < fraglen)
- continue;
-
- for (p = pkt->pkt_ip_data; p < pkt->pkt_end; ) {
- new = pkt_new();
- memcpy(new->pkt_ip, pkt->pkt_ip, hl);
- new->pkt_ip_data = new->pkt_eth_data + hl;
-
- p1 = p, p2 = NULL;
- off = (p - pkt->pkt_ip_data) >> 3;
- if (ip_frag_data.overlap != 0 && (off & 1) != 0 &&
- p + (fraglen << 1) < pkt->pkt_end) {
- rand_strset(ip_frag_data.rnd, tmp.pkt_buf,
- fraglen);
- if (ip_frag_data.overlap == FAVOR_OLD) {
- p1 = p + fraglen;
- p2 = tmp.pkt_buf;
- } else if (ip_frag_data.overlap == FAVOR_NEW) {
- p1 = tmp.pkt_buf;
- p2 = p + fraglen;
- }
- new->pkt_ip->ip_off = htons(IP_MF |
- (off + (fraglen >> 3)));
- } else {
- new->pkt_ip->ip_off = htons(off |
- ((p + fraglen < pkt->pkt_end) ? IP_MF: 0));
- }
- new->pkt_ip->ip_len = htons(hl + fraglen);
- ip_checksum(new->pkt_ip, hl + fraglen);
-
- memcpy(new->pkt_ip_data, p1, fraglen);
- new->pkt_end = new->pkt_ip_data + fraglen;
- TAILQ_INSERT_BEFORE(pkt, new, pkt_next);
- if (p2 != NULL) {
- new = pkt_dup(new);
- new->pkt_ts.tv_usec = 1;
- new->pkt_ip->ip_off = htons(IP_MF | off);
- new->pkt_ip->ip_len = htons(hl + (fraglen<<1));
- ip_checksum(new->pkt_ip, hl + (fraglen<<1));
-
- memcpy(new->pkt_ip_data, p, fraglen);
- memcpy(new->pkt_ip_data+fraglen, p2, fraglen);
- new->pkt_end = new->pkt_ip_data + (fraglen<<1);
- TAILQ_INSERT_BEFORE(pkt, new, pkt_next);
- p += (fraglen << 1);
- } else
- p += fraglen;
-
- if ((fraglen = pkt->pkt_end - p) > ip_frag_data.size)
- fraglen = ip_frag_data.size;
- }
- TAILQ_REMOVE(pktq, pkt, pkt_next);
- pkt_free(pkt);
- }
- return (0);
- }
- struct mod mod_ip_frag = {
- "ip_frag", /* name */
- "ip_frag <size> [old|new]", /* usage */
- ip_frag_open, /* open */
- ip_frag_apply, /* apply */
- ip_frag_close /* close */
- };
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