myip_options.c

一个基于linux的TCP/IP协议栈的实现

void myip_rt_get_source(u8 *addr, struct rtable *rt);
void myip_options_build(struct sk_buff * skb, struct ip_options * opt,
				u32 daddr, struct rtable *rt, int is_frag) 
{
	unsigned char * iph = skb->nh.raw;

	memcpy(&(IPCB(skb)->opt), opt, sizeof(struct ip_options));
	memcpy(iph+sizeof(struct iphdr), opt->__data, opt->optlen);
	opt = &(IPCB(skb)->opt);
	opt->is_data = 0;

	if (opt->srr)
		memcpy(iph+opt->srr+iph[opt->srr+1]-4, &daddr, 4);

	if (!is_frag) {
		if (opt->rr_needaddr)
			myip_rt_get_source(iph+opt->rr+iph[opt->rr+2]-5, rt);
		if (opt->ts_needaddr)
			myip_rt_get_source(iph+opt->ts+iph[opt->ts+2]-9, rt);
		if (opt->ts_needtime) {
			struct timeval tv;
			__u32 midtime;
			do_gettimeofday(&tv);
			midtime = htonl((tv.tv_sec % 86400) * 1000 + tv.tv_usec / 1000);
			memcpy(iph+opt->ts+iph[opt->ts+2]-5, &midtime, 4);
		}
		return;
	}
	if (opt->rr) {
		memset(iph+opt->rr, IPOPT_NOP, iph[opt->rr+1]);
		opt->rr = 0;
		opt->rr_needaddr = 0;
	}
	if (opt->ts) {
		memset(iph+opt->ts, IPOPT_NOP, iph[opt->ts+1]);
		opt->ts = 0;
		opt->ts_needaddr = opt->ts_needtime = 0;
	}
}

unsigned myinet_addr_type(u32 addr);
int myip_options_echo(struct ip_options * dopt, struct sk_buff * skb) 
{
	struct ip_options *sopt;
	unsigned char *sptr, *dptr;
	int soffset, doffset;
	int	optlen;
	u32	daddr;

	memset(dopt, 0, sizeof(struct ip_options));

	dopt->is_data = 1;

	sopt = &(IPCB(skb)->opt);

	if (sopt->optlen == 0) {
		dopt->optlen = 0;
		return 0;
	}

	sptr = skb->nh.raw;
	dptr = dopt->__data;

	if (skb->dst)
		daddr = ((struct rtable*)skb->dst)->rt_spec_dst;
	else
		daddr = skb->nh.iph->daddr;

	if (sopt->rr) {
		optlen  = sptr[sopt->rr+1];
		soffset = sptr[sopt->rr+2];
		dopt->rr = dopt->optlen + sizeof(struct iphdr);
		memcpy(dptr, sptr+sopt->rr, optlen);
		if (sopt->rr_needaddr && soffset <= optlen) {
			if (soffset + 3 > optlen)
				return -EINVAL;
			dptr[2] = soffset + 4;
			dopt->rr_needaddr = 1;
		}
		dptr += optlen;
		dopt->optlen += optlen;
	}
	if (sopt->ts) {
		optlen = sptr[sopt->ts+1];
		soffset = sptr[sopt->ts+2];
		dopt->ts = dopt->optlen + sizeof(struct iphdr);
		memcpy(dptr, sptr+sopt->ts, optlen);
		if (soffset <= optlen) {
			if (sopt->ts_needaddr) {
				if (soffset + 3 > optlen)
					return -EINVAL;
				dopt->ts_needaddr = 1;
				soffset += 4;
			}
			if (sopt->ts_needtime) {
				if (soffset + 3 > optlen)
					return -EINVAL;
				if ((dptr[3]&0xF) != IPOPT_TS_PRESPEC) {
					dopt->ts_needtime = 1;
					soffset += 4;
				} else {
					dopt->ts_needtime = 0;

					if (soffset + 8 <= optlen) {
						__u32 addr;

						memcpy(&addr, sptr+soffset-1, 4);
						if( myinet_addr_type(addr) != RTN_LOCAL ){
							dopt->ts_needtime = 1;
							soffset += 8;
						}
					}
				}
			}
			dptr[2] = soffset;
		}
		dptr += optlen;
		dopt->optlen += optlen;
	}
	if (sopt->srr) {
		unsigned char * start = sptr+sopt->srr;
		u32 faddr;

		optlen  = start[1];
		soffset = start[2];
		doffset = 0;
		if (soffset > optlen)
			soffset = optlen + 1;
		soffset -= 4;
		if (soffset > 3) {
			memcpy(&faddr, &start[soffset-1], 4);
			for (soffset-=4, doffset=4; soffset > 3; soffset-=4, doffset+=4)
				memcpy(&dptr[doffset-1], &start[soffset-1], 4);
			if (memcmp(&skb->nh.iph->saddr, &start[soffset+3], 4) == 0)
				doffset -= 4;
		}
		if (doffset > 3) {
			memcpy(&start[doffset-1], &daddr, 4);
			dopt->faddr = faddr;
			dptr[0] = start[0];
			dptr[1] = doffset+3;
			dptr[2] = 4;
			dptr += doffset+3;
			dopt->srr = dopt->optlen + sizeof(struct iphdr);
			dopt->optlen += doffset+3;
			dopt->is_strictroute = sopt->is_strictroute;
		}
	}
	while (dopt->optlen & 3) {
		*dptr++ = IPOPT_END;
		dopt->optlen++;
	}
	return 0;
}