static int whine_if_too_big(struct packet *in, struct packet *out)
{
unsigned int len;
unsigned int mtu;
if (pkt_l3_proto(in) == L3PROTO_IPV4 && !is_dont_fragment_set(pkt_ip4_hdr(in)))
return 0;
len = pkt_len(out);
mtu = get_nexthop_mtu(out);
if (len > mtu) {
/*
* We don't have to worry about ICMP errors causing this because the translate code already
* truncates them.
*/
log_debug("Packet is too big (len: %u, mtu: %u).", len, mtu);
switch (pkt_l3_proto(out)) {
case L3PROTO_IPV6:
mtu -= 20;
break;
case L3PROTO_IPV4:
mtu += 20;
break;
}
icmp64_send(out, ICMPERR_FRAG_NEEDED, mtu);
return -EINVAL;
}
return 0;
}
static bool test_function_is_dont_fragment_set(void)
{
struct iphdr hdr;
bool success = true;
hdr.frag_off = cpu_to_be16(0x0000);
success &= assert_equals_u16(0, is_dont_fragment_set(&hdr), "All zeroes");
hdr.frag_off = cpu_to_be16(0x4000);
success &= assert_equals_u16(1, is_dont_fragment_set(&hdr), "All zeroes except DF");
hdr.frag_off = cpu_to_be16(0xFFFF);
success &= assert_equals_u16(1, is_dont_fragment_set(&hdr), "All ones");
hdr.frag_off = cpu_to_be16(0xBFFF);
success &= assert_equals_u16(0, is_dont_fragment_set(&hdr), "All ones except DF");
return success;
}
static bool ipv4_validate_packet_len(struct sk_buff *skb_in, struct sk_buff *skb_out)
{
struct iphdr *ip4_hdr = ip_hdr(skb_out);
if (skb_out->len <= skb_out->dev->mtu)
return true;
if (ip4_hdr->protocol == IPPROTO_ICMP) {
struct icmphdr *icmp4_hdr = icmp_hdr(skb_out);
if (is_icmp4_error(icmp4_hdr->type)) {
int new_packet_len = skb_out->dev->mtu;
skb_trim(skb_out, new_packet_len);
ip4_hdr->tot_len = cpu_to_be16(new_packet_len);
ip4_hdr->check = 0;
ip4_hdr->check = ip_fast_csum(ip4_hdr, ip4_hdr->ihl);
icmp4_hdr->checksum = 0;
icmp4_hdr->checksum = ip_compute_csum(icmp4_hdr, new_packet_len - 4 * ip4_hdr->ihl);
return true;
}
}
if (is_dont_fragment_set(ip4_hdr)) {
unsigned int ipv6_mtu = skb_in->dev->mtu;
unsigned int ipv4_mtu = skb_out->dev->mtu;
log_debug("Packet is too large for the outgoing MTU and the DF flag is set. Dropping...");
icmpv6_send(skb_in, ICMPV6_PKT_TOOBIG, 0, cpu_to_be32(min_uint(ipv4_mtu, ipv6_mtu - 20)));
return false;
}
/* The kernel will fragment it. */
return true;
}