pf_check_proto_cksum(): simplify ICMP checksum verification

[Lawrence Teo]

This diff simplifies the verification of ICMP checksums in
pf_check_proto_cksum() by letting it use the same in4_cksum() call that
is used for TCP and UDP checksums.

As a bonus, since in4_cksum() doesn't need that m_data/m_len dance the
code becomes much shorter as well.

OK?


Index: pf.c
===================================================================
RCS file: /cvs/src/sys/net/pf.c,v
retrieving revision 1.865
diff -u -p -U10 -r1.865 pf.c
--- pf.c        22 Jan 2014 04:33:34 -0000      1.865
+++ pf.c        22 Jan 2014 22:33:23 -0000
@@ -5875,37 +5875,25 @@ pf_check_proto_cksum(struct pf_pdesc *pd
                return (0);
        }
        if (pd->m->m_pkthdr.csum_flags & flag_bad || off < sizeof(struct ip) ||
            pd->m->m_pkthdr.len < off + len) {
                pd->csum_status = PF_CSUM_BAD;
                return (1);
        }
        switch (af) {
 #ifdef INET
        case AF_INET:
-               if (p == IPPROTO_ICMP) {
-                       if (pd->m->m_len < off) {
-                               pd->csum_status = PF_CSUM_BAD;
-                               return (1);
-                       }
-                       pd->m->m_data += off;
-                       pd->m->m_len -= off;
-                       sum = in_cksum(pd->m, len);
-                       pd->m->m_data -= off;
-                       pd->m->m_len += off;
-               } else {
-                       if (pd->m->m_len < sizeof(struct ip)) {
-                               pd->csum_status = PF_CSUM_BAD;
-                               return (1);
-                       }
-                       sum = in4_cksum(pd->m, p, off, len);
+               if (pd->m->m_len < sizeof(struct ip)) {
+                       pd->csum_status = PF_CSUM_BAD;
+                       return (1);
                }
+               sum = in4_cksum(pd->m, (p == IPPROTO_ICMP ? 0 : p), off, len);
                break;
 #endif /* INET */
 #ifdef INET6
        case AF_INET6:
                if (pd->m->m_len < sizeof(struct ip6_hdr)) {
                        pd->csum_status = PF_CSUM_BAD;
                        return (1);
                }
                sum = in6_cksum(pd->m, p, off, len);
                break;