[PATCH net-next v2 1/2] net: add missing syncookie statistics for BPF custom syncookies

Jiayuan Chen
2026-04-11T01:32:50Z

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_SYSCALL guard around struct bpf_tcp_req_attrs.
This struct is referenced by bpf_sk_assign_tcp_reqsk() in
net/core/filter.c which is compiled unconditionally, so wrapping
the definition in a config guard could cause build failures when
CONFIG_BPF_SYSCALL=n.

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>
---
No functional bug here — CONFIG_BPF is always enabled under
CONFIG_NET, so the existing code compiles and works correctly.
This is a cleanup and improvement, no backport needed.

Added a selftest, suggested by Kuniyuki Iwashima.
---
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 6156d1d068e1..570a8836c2ba 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -598,7 +598,6 @@ 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;
@@ -612,7 +611,6 @@ struct bpf_tcp_req_attrs {
u8 usec_ts_ok;
u8 reserved[3];
};
-#endif

#ifdef CONFIG_SYN_COOKIES

@@ -715,13 +713,14 @@ 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 f1474598d2c8..d685631438cb 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -295,8 +295,9 @@ 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);

@@ -306,6 +307,9 @@ 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 4f6f0d751d6c..111d7a41d957 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