Commit 695751e3 authored by Kuniyuki Iwashima's avatar Kuniyuki Iwashima Committed by Alexei Starovoitov
Browse files

bpf: tcp: Handle BPF SYN Cookie in cookie_v[46]_check(). 



We will support arbitrary SYN Cookie with BPF in the following
patch.

If BPF prog validates ACK and kfunc allocates a reqsk, it will
be carried to cookie_[46]_check() as skb->sk.  If skb->sk is not
NULL, we call cookie_bpf_check().

Then, we clear skb->sk and skb->destructor, which are needed not
to hold refcnt for reqsk and the listener.  See the following patch
for details.

After that, we finish initialisation for the remaining fields with
cookie_tcp_reqsk_init().

Note that the server side WScale is set only for non-BPF SYN Cookie.

Signed-off-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240115205514.68364-5-kuniyu@amazon.com


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 8b5ac68f

include/net/tcp.h

+20 −0
Original line number Diff line number Diff line
@@ -599,6 +599,26 @@ static inline bool cookie_ecn_ok(const struct net *net, const struct dst_entry * 
		dst_feature(dst, RTAX_FEATURE_ECN);

}



#if IS_ENABLED(CONFIG_BPF)

static inline bool cookie_bpf_ok(struct sk_buff *skb)

{

	return skb->sk;

}



struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb);

#else

static inline bool cookie_bpf_ok(struct sk_buff *skb)

{

	return false;

}



static inline struct request_sock *cookie_bpf_check(struct net *net, struct sock *sk,

						    struct sk_buff *skb)

{

	return NULL;

}

#endif



/* From net/ipv6/syncookies.c */

int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th);

struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);

net/ipv4/syncookies.c

+27 −4
Original line number Diff line number Diff line
@@ -295,6 +295,24 @@ static int cookie_tcp_reqsk_init(struct sock *sk, struct sk_buff *skb, 
	return 0;

}



#if IS_ENABLED(CONFIG_BPF)

struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb)

{

	struct request_sock *req = inet_reqsk(skb->sk);



	skb->sk = NULL;

	skb->destructor = NULL;



	if (cookie_tcp_reqsk_init(sk, skb, req)) {

		reqsk_free(req);

		req = NULL;

	}



	return req;

}

EXPORT_SYMBOL_GPL(cookie_bpf_check);

#endif



struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,

					    struct sock *sk, struct sk_buff *skb,

					    struct tcp_options_received *tcp_opt,
@@ -395,9 +413,13 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) 
	    !th->ack || th->rst)

		goto out;



	if (cookie_bpf_ok(skb)) {

		req = cookie_bpf_check(sk, skb);

	} else {

		req = cookie_tcp_check(net, sk, skb);

		if (IS_ERR(req))

			goto out;

	}

	if (!req)

		goto out_drop;
@@ -445,6 +467,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) 
				  ireq->wscale_ok, &rcv_wscale,

				  dst_metric(&rt->dst, RTAX_INITRWND));



	if (!req->syncookie)

		ireq->rcv_wscale = rcv_wscale;

	ireq->ecn_ok &= cookie_ecn_ok(net, &rt->dst);

net/ipv6/syncookies.c

+9 −4
Original line number Diff line number Diff line
@@ -182,9 +182,13 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 
	    !th->ack || th->rst)

		goto out;



	if (cookie_bpf_ok(skb)) {

		req = cookie_bpf_check(sk, skb);

	} else {

		req = cookie_tcp_check(net, sk, skb);

		if (IS_ERR(req))

			goto out;

	}

	if (!req)

		goto out_drop;
@@ -247,6 +251,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 
				  ireq->wscale_ok, &rcv_wscale,

				  dst_metric(dst, RTAX_INITRWND));



	if (!req->syncookie)

		ireq->rcv_wscale = rcv_wscale;

	ireq->ecn_ok &= cookie_ecn_ok(net, dst);