Re: [PATCH v2 net] tcp: avoid the lookup process failing to get sk in ehash table

[Eric Dumazet]

On Sat, Jan 14, 2023 at 2:27 PM Jason Xing <kerneljasonxing@xxxxxxxxx> wrote:
>
> From: Jason Xing <kernelxing@xxxxxxxxxxx>
>
>
> Fixes: 5e0724d027f0 ("tcp/dccp: fix hashdance race for passive sessions")
> Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/20230112065336.41034-1-kerneljasonxing@xxxxxxxxx/
> ---
> v2:
> 1) adding the sk node into the tail of list to prevent the race.
> 2) fix the race condition when handling time-wait socket hashdance.
> ---
>  net/ipv4/inet_hashtables.c    | 10 ++++++++++
>  net/ipv4/inet_timewait_sock.c |  6 +++---
>  2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index 24a38b56fab9..b0b54ad55507 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -650,7 +650,16 @@ bool inet_ehash_insert(struct sock *sk, struct sock *osk, bool *found_dup_sk)
>         spin_lock(lock);
>         if (osk) {
>                 WARN_ON_ONCE(sk->sk_hash != osk->sk_hash);
> +               if (sk_hashed(osk))


nit: this should be:

if (sk_hashed(osk)) {  [1]
    /* multi-line ....
     * .... comment.
     */
   ret = sk_nulls_del_node_init_rcu(osk);
   goto unlock;
}
if (found_dup_sk) {  [2]

1) parentheses needed in [1]
2) No else if in [2], since you added a "goto unlock;"

> +                       /* Before deleting the node, we insert a new one to make
> +                        * sure that the look-up-sk process would not miss either
> +                        * of them and that at least one node would exist in ehash
> +                        * table all the time. Otherwise there's a tiny chance
> +                        * that lookup process could find nothing in ehash table.
> +                        */
> +                       __sk_nulls_add_node_tail_rcu(sk, list);
>                 ret = sk_nulls_del_node_init_rcu(osk);
> +               goto unlock;
>         } else if (found_dup_sk) {
>                 *found_dup_sk = inet_ehash_lookup_by_sk(sk, list);
>                 if (*found_dup_sk)
> @@ -660,6 +669,7 @@ bool inet_ehash_insert(struct sock *sk, struct sock *osk, bool *found_dup_sk)
>         if (ret)
>                 __sk_nulls_add_node_rcu(sk, list);
>
> +unlock:
>         spin_unlock(lock);

Thanks.