linux-kernel - Re: [PATCH 4/7] net/tcp: Reset TCP-AO cached keys on listen() syscall

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Date:   Tue, 21 Nov 2023 09:18:10 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     David Ahern <dsahern@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Francesco Ruggeri <fruggeri05@...il.com>,
        Salam Noureddine <noureddine@...sta.com>,
        Simon Horman <horms@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH 4/7] net/tcp: Reset TCP-AO cached keys on listen() syscall

On Tue, Nov 21, 2023 at 3:01 AM Dmitry Safonov <dima@...sta.com> wrote:
>
> TCP_LISTEN sockets are not connected to any peer, so having
> current_key/rnext_key doesn't make sense.
>
> The userspace may falter over this issue by setting current or rnext
> TCP-AO key before listen() syscall. setsockopt(TCP_AO_DEL_KEY) doesn't
> allow removing a key that is in use (in accordance to RFC 5925), so
> it might be inconvenient to have keys that can be destroyed only with
> listener socket.

I think this is the wrong way to solve this issue. listen() should not
mess with anything else than socket state.

>
> Fixes: 4954f17ddefc ("net/tcp: Introduce TCP_AO setsockopt()s")
> Signed-off-by: Dmitry Safonov <dima@...sta.com>
> ---
>  include/net/tcp_ao.h |  5 +++++
>  net/ipv4/af_inet.c   |  1 +
>  net/ipv4/tcp_ao.c    | 14 ++++++++++++++
>  3 files changed, 20 insertions(+)
>
> diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
> index 647781080613..e36057ca5ed8 100644
> --- a/include/net/tcp_ao.h
> +++ b/include/net/tcp_ao.h
> @@ -270,6 +270,7 @@ int tcp_v6_ao_synack_hash(char *ao_hash, struct tcp_ao_key *ao_key,
>  void tcp_ao_established(struct sock *sk);
>  void tcp_ao_finish_connect(struct sock *sk, struct sk_buff *skb);
>  void tcp_ao_connect_init(struct sock *sk);
> +void tcp_ao_listen(struct sock *sk);
>  void tcp_ao_syncookie(struct sock *sk, const struct sk_buff *skb,
>                       struct tcp_request_sock *treq,
>                       unsigned short int family, int l3index);
> @@ -330,6 +331,10 @@ static inline void tcp_ao_connect_init(struct sock *sk)
>  {
>  }
>
> +static inline void tcp_ao_listen(struct sock *sk)
> +{
> +}
> +
>  static inline int tcp_ao_get_mkts(struct sock *sk, sockptr_t optval, sockptr_t optlen)
>  {
>         return -ENOPROTOOPT;
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index fb81de10d332..a08d1266344f 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -200,6 +200,7 @@ int __inet_listen_sk(struct sock *sk, int backlog)
>          * we can only allow the backlog to be adjusted.
>          */
>         if (old_state != TCP_LISTEN) {
> +               tcp_ao_listen(sk);

Ouch...

Please add your hook in tcp_disconnect() instead of this layering violation.

I think you missed the fact that applications can call listen(fd,
backlog) multiple times,
if they need to dynamically adjust backlog.