Hello,
why is it that I cannot get the conntrack ID when I set up a callback
function for DESTROY events with libnetfilter_conntrack?
When I do
int id = nfct_get_attr_u32(ct, ATTR_ID);
printf("delete ID: %d\n", id);
in my callback function. The id I get is always 0.
It works for conntrack dumps but not for events it seems.
The other question I have is the following.
I need to port a kernelspace netfilter module to userspace. It deals
with udp and icmp packets, and in kernelspace I have the match function
as a callback and in that match function I grab the corresponding
conntrack tuple for the incoming packet to get the conntrack id. With
this id I can search a list, if this connection is already in that list,
and can update information in that list or add the connection to the
list if it is not yet in that list.
I also have a notifier callback function where I get notified when a
connection was deleted. I need this to get the id of the deleted
connection and delete it as well in my list with connections.
Now the question is, how I can do this in userspace. I managed to get
the match function from kernelspace ported to userspace by using
libnetfilter_queue API. But to implement the delete notifier and to get
the conntrack id I need to use libnetfilter_conntrack API where the
problems arise.
I need
while ((rv = recv(fd, buf, sizeof(buf), 0)) && rv >= 0) {
nfq_handle_packet(h, buf, rv);
}
to handle packets with my libnetfilter_queue callback function. But if I
want to get notified by conntrack for delete events I need nfct_catch,
which also blocks my program.
So my question is, if I need to spawn multiple threads to get it done or
if there is another solution?
thanks in advance,
Thomas Mader
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