netdev - Re: [PATCH v1 net 14/15] tcp: Fix data-races around sysctl_tcp

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Date:   Sun, 17 Jul 2022 08:20:19 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...nel.org>,
        Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 net 14/15] tcp: Fix data-races around sysctl_tcp_fastopen.

On Fri, Jul 15, 2022 at 10:21 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> While reading sysctl_tcp_fastopen, it can be changed concurrently.
> Thus, we need to add READ_ONCE() to its readers.
>
> Fixes: 2100c8d2d9db ("net-tcp: Fast Open base")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
> CC: Yuchung Cheng <ycheng@...gle.com>
Thanks for the improvement

Acked-by: Yuchung Cheng <ycheng@...gle.com>

> ---
>  net/ipv4/af_inet.c      | 2 +-
>  net/ipv4/tcp.c          | 6 ++++--
>  net/ipv4/tcp_fastopen.c | 4 ++--
>  3 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 4bc24f9e38b3..59a0c5406fc1 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -217,7 +217,7 @@ int inet_listen(struct socket *sock, int backlog)
>                  * because the socket was in TCP_LISTEN state previously but
>                  * was shutdown() rather than close().
>                  */
> -               tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
> +               tcp_fastopen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen);
>                 if ((tcp_fastopen & TFO_SERVER_WO_SOCKOPT1) &&
>                     (tcp_fastopen & TFO_SERVER_ENABLE) &&
>                     !inet_csk(sk)->icsk_accept_queue.fastopenq.max_qlen) {
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index b1b1bcbc4f60..2faaaaf540ac 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1150,7 +1150,8 @@ static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
>         struct sockaddr *uaddr = msg->msg_name;
>         int err, flags;
>
> -       if (!(sock_net(sk)->ipv4.sysctl_tcp_fastopen & TFO_CLIENT_ENABLE) ||
> +       if (!(READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen) &
> +             TFO_CLIENT_ENABLE) ||
>             (uaddr && msg->msg_namelen >= sizeof(uaddr->sa_family) &&
>              uaddr->sa_family == AF_UNSPEC))
>                 return -EOPNOTSUPP;
> @@ -3617,7 +3618,8 @@ static int do_tcp_setsockopt(struct sock *sk, int level, int optname,
>         case TCP_FASTOPEN_CONNECT:
>                 if (val > 1 || val < 0) {
>                         err = -EINVAL;
> -               } else if (net->ipv4.sysctl_tcp_fastopen & TFO_CLIENT_ENABLE) {
> +               } else if (READ_ONCE(net->ipv4.sysctl_tcp_fastopen) &
> +                          TFO_CLIENT_ENABLE) {
>                         if (sk->sk_state == TCP_CLOSE)
>                                 tp->fastopen_connect = val;
>                         else
> diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> index fdbcf2a6d08e..0acdb5473850 100644
> --- a/net/ipv4/tcp_fastopen.c
> +++ b/net/ipv4/tcp_fastopen.c
> @@ -332,7 +332,7 @@ static bool tcp_fastopen_no_cookie(const struct sock *sk,
>                                    const struct dst_entry *dst,
>                                    int flag)
>  {
> -       return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
> +       return (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen) & flag) ||
>                tcp_sk(sk)->fastopen_no_cookie ||
>                (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
>  }
> @@ -347,7 +347,7 @@ struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
>                               const struct dst_entry *dst)
>  {
>         bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
> -       int tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
> +       int tcp_fastopen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen);
>         struct tcp_fastopen_cookie valid_foc = { .len = -1 };
>         struct sock *child;
>         int ret = 0;
> --
> 2.30.2
>