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: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
---
include/net/tcp.h | 20 ++++++++++++++++++++
net/ipv4/syncookies.c | 31 +++++++++++++++++++++++++++----
net/ipv6/syncookies.c | 13 +++++++++----
3 files changed, 56 insertions(+), 8 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 07dd18e2f3af..a63916f41f77 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -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);
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 981944c22820..be88bf586ff9 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -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;
- req = cookie_tcp_check(net, sk, skb);
- if (IS_ERR(req))
- 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;
@@ -445,7 +467,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
ireq->wscale_ok, &rcv_wscale,
dst_metric(&rt->dst, RTAX_INITRWND));
- ireq->rcv_wscale = rcv_wscale;
+ if (!req->syncookie)
+ ireq->rcv_wscale = rcv_wscale;
ireq->ecn_ok &= cookie_ecn_ok(net, &rt->dst);
ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst);
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index c8d2ca27220c..6b9c69278819 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -182,9 +182,13 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
!th->ack || th->rst)
goto out;
- req = cookie_tcp_check(net, sk, skb);
- if (IS_ERR(req))
- 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;
@@ -247,7 +251,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
ireq->wscale_ok, &rcv_wscale,
dst_metric(dst, RTAX_INITRWND));
- ireq->rcv_wscale = rcv_wscale;
+ if (!req->syncookie)
+ ireq->rcv_wscale = rcv_wscale;
ireq->ecn_ok &= cookie_ecn_ok(net, dst);
ret = tcp_get_cookie_sock(sk, skb, req, dst);
--
2.30.2
