- struct iphdr *iph;
- struct udphdr *udph;
- struct icmphdr *icmph;
- struct sk_buff *nskb;
- u32 saddr;
- u8 tos;
- int hh_len, length;
- struct rtable *rt = (struct rtable*)skb_in->dst;
- unsigned char *data;
-
- if (!rt)
- return;
-
- /* FIXME: Use sysctl number. --RR */
- if (!xrlim_allow(&rt->u.dst, 1*HZ))
- return;
-
- iph = skb_in->nh.iph;
-
- /* No replies to physical multicast/broadcast */
- if (skb_in->pkt_type!=PACKET_HOST)
- return;
-
- /* Now check at the protocol level */
- if (rt->rt_flags&(RTCF_BROADCAST|RTCF_MULTICAST))
- return;
-
- /* Only reply to fragment 0. */
- if (iph->frag_off&htons(IP_OFFSET))
- return;
-
- /* Ensure we have at least 8 bytes of proto header. */
- if (skb_in->len < skb_in->nh.iph->ihl*4 + 8)
- return;
-
- /* if UDP checksum is set, verify it's correct */
- if (iph->protocol == IPPROTO_UDP
- && skb_in->tail-(u8*)iph >= sizeof(struct udphdr)) {
- int datalen = skb_in->len - (iph->ihl<<2);
- udph = (struct udphdr *)((char *)iph + (iph->ihl<<2));
- if (udph->check
- && csum_tcpudp_magic(iph->saddr, iph->daddr,
- datalen, IPPROTO_UDP,
- csum_partial((char *)udph, datalen,
- 0)) != 0)
- return;
- }
-
- /* If we send an ICMP error to an ICMP error a mess would result.. */
- if (iph->protocol == IPPROTO_ICMP
- && skb_in->tail-(u8*)iph >= sizeof(struct icmphdr)) {
- icmph = (struct icmphdr *)((char *)iph + (iph->ihl<<2));
-
- if (skb_copy_bits(skb_in, skb_in->nh.iph->ihl*4,
- icmph, sizeof(*icmph)) < 0)
- return;
-
- /* Between echo-reply (0) and timestamp (13),
- everything except echo-request (8) is an error.
- Also, anything greater than NR_ICMP_TYPES is
- unknown, and hence should be treated as an error... */
- if ((icmph->type < ICMP_TIMESTAMP
- && icmph->type != ICMP_ECHOREPLY
- && icmph->type != ICMP_ECHO)
- || icmph->type > NR_ICMP_TYPES)
- return;
- }
-
- saddr = iph->daddr;
- if (!(rt->rt_flags & RTCF_LOCAL))
- saddr = 0;
-
- tos = (iph->tos & IPTOS_TOS_MASK) | IPTOS_PREC_INTERNETCONTROL;
-
- {
- struct flowi fl = { .nl_u = { .ip4_u =
- { .daddr = skb_in->nh.iph->saddr,
- .saddr = saddr,
- .tos = RT_TOS(tos) } } };
- if (ip_route_output_key(&rt, &fl))
- return;
- }
- /* RFC says return as much as we can without exceeding 576 bytes. */
- length = skb_in->len + sizeof(struct iphdr) + sizeof(struct icmphdr);
-
- if (length > dst_pmtu(&rt->u.dst))
- length = dst_pmtu(&rt->u.dst);
- if (length > 576)
- length = 576;
-
- hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
-
- nskb = alloc_skb(hh_len + length, GFP_ATOMIC);
- if (!nskb) {
- ip_rt_put(rt);
- return;
- }
-
- nskb->priority = 0;
- nskb->dst = &rt->u.dst;
- skb_reserve(nskb, hh_len);
-
- /* Set up IP header */
- iph = nskb->nh.iph
- = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
- iph->version=4;
- iph->ihl=5;
- iph->tos=tos;
- iph->tot_len = htons(length);
-
- /* PMTU discovery never applies to ICMP packets. */
- iph->frag_off = 0;
-
- iph->ttl = MAXTTL;
- ip_select_ident(iph, &rt->u.dst, NULL);
- iph->protocol=IPPROTO_ICMP;
- iph->saddr=rt->rt_src;
- iph->daddr=rt->rt_dst;
- iph->check=0;
- iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
-
- /* Set up ICMP header. */
- icmph = nskb->h.icmph
- = (struct icmphdr *)skb_put(nskb, sizeof(struct icmphdr));
- icmph->type = ICMP_DEST_UNREACH;
- icmph->code = code;
- icmph->un.gateway = 0;
- icmph->checksum = 0;
-
- /* Copy as much of original packet as will fit */
- data = skb_put(nskb,
- length - sizeof(struct iphdr) - sizeof(struct icmphdr));
-
- skb_copy_bits(skb_in, 0, data,
- length - sizeof(struct iphdr) - sizeof(struct icmphdr));
-
- icmph->checksum = ip_compute_csum((unsigned char *)icmph,
- length - sizeof(struct iphdr));
-
- connection_attach(nskb, skb_in->nfct);
-
- NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
- ip_finish_output);