Re: [PATCH net-next v1] net: add missing syncookie statistics for BPF custom syncookies

[Kuniyuki Iwashima]

On Thu, Apr 9, 2026 at 5:41 AM Jiayuan Chen <jiayuan.chen@xxxxxxxxx> wrote:
>
> 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.

Can you add SNMP test in tcp_custom_syncookie.c by checking
the delta before connect_to_fd() and after accept() ?


>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> ---
> 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.
> ---
>  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
>