[PATCH bpf-next v4 1/2] net: add missing syncookie statistics for BPF custom syncookies

[Jiayuan Chen <jiayuan.chen@linux.dev>]

1. Replace IS_ENABLED(CONFIG_BPF) with CONFIG_BPF_SYSCALL for
   cookie_bpf_ok() and cookie_bpf_check(). CONFIG_BPF is selected by
   CONFIG_NET unconditionally, so IS_ENABLED(CONFIG_BPF) is always
   true and provides no real guard. CONFIG_BPF_SYSCALL is the correct
   config for BPF program functionality.

2. Remove the CONFIG_BPF guard around struct bpf_tcp_req_attrs.
   Since CONFIG_BPF is always selected by CONFIG_NET the guard is a
   no-op, and the struct is referenced by bpf_sk_assign_tcp_reqsk()
   in net/core/filter.c which is compiled unconditionally, so its
   visibility is not actually conditional on BPF being enabled.

3. Fix mismatched declaration of cookie_bpf_check() between the
   CONFIG_BPF_SYSCALL and stub paths: the real definition takes
   'struct net *net' but the declaration in the header did not.
   Add the net parameter to the declaration and all call sites.

4. Add missing LINUX_MIB_SYNCOOKIESRECV and LINUX_MIB_SYNCOOKIESFAILED
   statistics in cookie_bpf_check(), so that BPF custom syncookie
   validation is accounted for in SNMP counters just like the
   non-BPF path.

Compile-tested with CONFIG_BPF_SYSCALL=y and CONFIG_BPF_SYSCALL
not set.

Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

---
To sashiko: We already called skb->sk = NULL before calling
reqsk_free(req). So there is no worry about skb->sk becoming
dangling pointer after cookie_tcp_reqsk_init() fails.
---
 include/net/tcp.h     |  7 +++----
 net/ipv4/syncookies.c | 10 +++++++---
 net/ipv6/syncookies.c |  2 +-
 3 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index ecbadcb3a7446..7d87bc2d21d17 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -599,7 +599,6 @@ struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
 					    struct tcp_options_received *tcp_opt,
 					    int mss, u32 tsoff);
 
-#if IS_ENABLED(CONFIG_BPF)
 struct bpf_tcp_req_attrs {
 	u32 rcv_tsval;
 	u32 rcv_tsecr;
@@ -613,7 +612,6 @@ struct bpf_tcp_req_attrs {
 	u8 usec_ts_ok;
 	u8 reserved[3];
 };
-#endif
 
 #ifdef CONFIG_SYN_COOKIES
 
@@ -716,13 +714,14 @@ 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)
+#ifdef CONFIG_BPF_SYSCALL
 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);
+struct request_sock *cookie_bpf_check(struct net *net, struct sock *sk,
+				      struct sk_buff *skb);
 #else
 static inline bool cookie_bpf_ok(struct sk_buff *skb)
 {
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index df479277fb801..9251d4a15c888 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -294,8 +294,9 @@ 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)
+#ifdef CONFIG_BPF_SYSCALL
+struct request_sock *cookie_bpf_check(struct net *net, struct sock *sk,
+				      struct sk_buff *skb)
 {
 	struct request_sock *req = inet_reqsk(skb->sk);
 
@@ -305,6 +306,9 @@ struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb)
 	if (cookie_tcp_reqsk_init(sk, skb, req)) {
 		reqsk_free(req);
 		req = NULL;
+		__NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESFAILED);
+	} else {
+		__NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESRECV);
 	}
 
 	return req;
@@ -419,7 +423,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 		goto out;
 
 	if (cookie_bpf_ok(skb)) {
-		req = cookie_bpf_check(sk, skb);
+		req = cookie_bpf_check(net, sk, skb);
 	} else {
 		req = cookie_tcp_check(net, sk, skb);
 		if (IS_ERR(req))
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 4f6f0d751d6c5..111d7a41d9573 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -190,7 +190,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		goto out;
 
 	if (cookie_bpf_ok(skb)) {
-		req = cookie_bpf_check(sk, skb);
+		req = cookie_bpf_check(net, sk, skb);
 	} else {
 		req = cookie_tcp_check(net, sk, skb);
 		if (IS_ERR(req))
-- 
2.43.0