Fixed broken ICMP error generation, unified conversion of IP header

fields between host and network byte order.  The details:

o icmp_error() now does not add IP header length.  This fixes the problem
  when icmp_error() is called from ip_forward().  In this case the ip_len
  of the original IP datagram returned with ICMP error was wrong.

o icmp_error() expects all three fields, ip_len, ip_id and ip_off in host
  byte order, so DTRT and convert these fields back to network byte order
  before sending a message.  This fixes the problem described in PR 16240
  and PR 20877 (ip_id field was returned in host byte order).

o ip_ttl decrement operation in ip_forward() was moved down to make sure
  that it does not corrupt the copy of original IP datagram passed later
  to icmp_error().

o A copy of original IP datagram in ip_forward() was made a read-write,
  independent copy.  This fixes the problem I first reported to Garrett
  Wollman and Bill Fenner and later put in audit trail of PR 16240:
  ip_output() (not always) converts fields of original datagram to network
  byte order, but because copy (mcopy) and its original (m) most likely
  share the same mbuf cluster, ip_output()'s manipulations on original
  also corrupted the copy.

o ip_output() now expects all three fields, ip_len, ip_off and (what is
  significant) ip_id in host byte order.  It was a headache for years that
  ip_id was handled differently.  The only compatibility issue here is the
  raw IP socket interface with IP_HDRINCL socket option set and a non-zero
  ip_id field, but ip.4 manual page was unclear on whether in this case
  ip_id field should be in host or network byte order.

1 files changed, 2 insertions, 1 deletions

diff --git a/sys/netinet/ip_mroute.c b/sys/netinet/ip_mroute.c
index 1d165f5..73ab039 100644
--- a/sys/netinet/ip_mroute.c
+++ b/sys/netinet/ip_mroute.c
@@ -1581,7 +1581,7 @@ encap_send(ip, vifp, m)
      */
     ip_copy = mtod(mb_copy, struct ip *);
     *ip_copy = multicast_encap_iphdr;
-    ip_copy->ip_id = htons(ip_id++);
+    ip_copy->ip_id = ip_id++;
     ip_copy->ip_len += len;
     ip_copy->ip_src = vifp->v_lcl_addr;
     ip_copy->ip_dst = vifp->v_rmt_addr;
@@ -1592,6 +1592,7 @@ encap_send(ip, vifp, m)
     ip = (struct ip *)((caddr_t)ip_copy + sizeof(multicast_encap_iphdr));
     --ip->ip_ttl;
     HTONS(ip->ip_len);
+    HTONS(ip->ip_id);
     HTONS(ip->ip_off);
     ip->ip_sum = 0;
     mb_copy->m_data += sizeof(multicast_encap_iphdr);