I'm writing a netfilter match extension (xtables-addons 1.33, kernel
2.6.35, .family=NFPROTO_UNSPEC) that needs to examine the source and
destination port numbers of all packets. The following code
successfully gets the port numbers for IPv4 TCP and UDP packets:
static bool xt_mymatch_mt(const struct sk_buff *skb,
struct xt_action_param *par)
{
const __be16 *pptr;
__be16 _ports[2];
int sport = 0;
int dport = 0;
if (par->fragoff == 0) {
pptr = skb_header_pointer(skb, par->thoff,
sizeof(_ports), _ports);
if (pptr != NULL) {
sport = ntohs(pptr[0]);
dport = ntohs(pptr[1]);
}
}
/* ...remaining code omitted... */
}
However, when I test this with "telnet ::1 1234", it does not work for
IPv6 TCP packets (I have not tried with IPv6 UDP packets yet). By
adding printk() statements, I've determined that par->fragoff is never 0
for my IPv6 TCP packets -- instead, it is large numbers such as
33569744, 2164528116, or 2164412871. However, par->in and par->out are
both correct. par->matchinfo, ipv6_hdr(skb)->saddr, and
ipv6_hdr(skb)->daddr are also all correct.
What am I doing wrong?
Thanks in advance for any help.
--
Mark Montague
mark@xxxxxxxxxxx
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