How to remove conntrack entry from within Linux kernel?

Question

I need to delete a conntrack entry in the kernel. There are numerous functions like nf_ct_delete and nf_ct_put. At the moment I use both on a skb->nfct (block on every tracked skb). It seems to work fine at first, but after some seconds the kernel just crashes.

My current code is as follows:

struct nf_conntrack *con = skb->nfct;
nf_conntrack_get(sub_conntrack);
//... do some stuff 
nf_ct_delete((struct nf_conn *) con, 0, 0);
nf_ct_put((struct nf_conn *) con);

Directly after execution of the delete and put statement, I check the entries with conntrack -L conntrack and they are gone (as expected). But after one minute or so, the system freezes. I guess conntrack starts some timers that crash when fired.

So my question is: How can I immediately delete everything for a specific connection? Including stopping any timers and cleaning up all state.

Answer 1

This is adapted from the netfilter code

int delete_nat_entry(u32 loc_ip, u32 rem_ip, u16 loc_port, u16 rem_port) {
        struct nf_conntrack_tuple_hash *h;
        struct nf_conntrack_tuple tuple;
        struct nf_conn *ct;

        memset(&tuple, 0, sizeof(tuple));

        //layer 3
        tuple.src.l3num = PF_INET;
        tuple.src.u3.ip = htonl(loc_ip);
        tuple.dst.u3.ip = htonl(rem_ip);

        //layer 4
        tuple.dst.protonum = IPPROTO_TCP;
        tuple.dst.dir = IP_CT_DIR_ORIGINAL;
        tuple.src.u.tcp.port = htons(loc_port);
        tuple.dst.u.tcp.port = htons(rem_port);

        h = nf_conntrack_find_get(&init_net, NF_CT_DEFAULT_ZONE, &tuple);
        if (!h) {
                debug_msg(KERN_INFO "cannot find conntrack tuple\n");
                return -ENOENT;
        }
        ct = nf_ct_tuplehash_to_ctrack(h);

        if (del_timer(&ct->timeout))
                nf_ct_delete(ct, 0, 0);

        nf_ct_put(ct);

        return 0;
}