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bpf: tcp: Support arbitrary SYN Cookie.

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This patch adds a new kfunc available at TC hook to support arbitrary
SYN Cookie.

The basic usage is as follows:

    struct bpf_tcp_req_attrs attrs = {
        .mss = mss,
        .wscale_ok = wscale_ok,
        .rcv_wscale = rcv_wscale, /* Server's WScale < 15 */
        .snd_wscale = snd_wscale, /* Client's WScale < 15 */
        .tstamp_ok = tstamp_ok,
        .rcv_tsval = tsval,
        .rcv_tsecr = tsecr, /* Server's Initial TSval */
        .usec_ts_ok = usec_ts_ok,
        .sack_ok = sack_ok,
        .ecn_ok = ecn_ok,
    }

    skc = bpf_skc_lookup_tcp(...);
    sk = (struct sock *)bpf_skc_to_tcp_sock(skc);
    bpf_sk_assign_tcp_reqsk(skb, sk, attrs, sizeof(attrs));
    bpf_sk_release(skc);

bpf_sk_assign_tcp_reqsk() takes skb, a listener sk, and struct
bpf_tcp_req_attrs and allocates reqsk and configures it.  Then,
bpf_sk_assign_tcp_reqsk() links reqsk with skb and the listener.

The notable thing here is that we do not hold refcnt for both reqsk
and listener.  To differentiate that, we mark reqsk->syncookie, which
is only used in TX for now.  So, if reqsk->syncookie is 1 in RX, it
means that the reqsk is allocated by kfunc.

When skb is freed, sock_pfree() checks if reqsk->syncookie is 1,
and in that case, we set NULL to reqsk->rsk_listener before calling
reqsk_free() as reqsk does not hold a refcnt of the listener.

When the TCP stack looks up a socket from the skb, we steal the
listener from the reqsk in skb_steal_sock() and create a full sk
in cookie_v[46]_check().

The refcnt of reqsk will finally be set to 1 in tcp_get_cookie_sock()
after creating a full sk.

Note that we can extend struct bpf_tcp_req_attrs in the future when
we add a new attribute that is determined in 3WHS.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240115205514.68364-6-kuniyu@amazon.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kuniyuki Iwashima
2024-01-15 12:55:13 -08:00
committed by Alexei Starovoitov
parent 695751e31a
commit e472f88891
3 changed files with 135 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
net/core/sock.c
View File

@@ -2582,8 +2582,18 @@ EXPORT_SYMBOL(sock_efree);
#ifdef CONFIG_INET
void sock_pfree(struct sk_buff *skb)
{
if (sk_is_refcounted(skb->sk))
sock_gen_put(skb->sk);
struct sock *sk = skb->sk;
if (!sk_is_refcounted(sk))
return;
if (sk->sk_state == TCP_NEW_SYN_RECV && inet_reqsk(sk)->syncookie) {
inet_reqsk(sk)->rsk_listener = NULL;
reqsk_free(inet_reqsk(sk));
return;
}
sock_gen_put(sk);
}
EXPORT_SYMBOL(sock_pfree);
#endif /* CONFIG_INET */