linux-kernel - Re: [PATCH] udp6: Fix race condition in udp6

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Date:   Fri, 26 May 2023 18:47:36 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Vlad Efanov <vefanov@...ras.ru>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH] udp6: Fix race condition in udp6_sendmsg & connect

On Fri, May 26, 2023 at 6:41 PM Vlad Efanov <vefanov@...ras.ru> wrote:
>
> sk_dst_set() is called by sk_setup_caps().
>
> sk_dst_set() replaces dst in socket using xchg() call and we still have
> two tasks use one socket but expect different dst in sk_dst_cache.
>
>
> __sk_dst_set() is rcu protected, but it checks for socket lock.
>
>
> static inline void
> __sk_dst_set(struct sock *sk, struct dst_entry *dst)
> {
>      struct dst_entry *old_dst;
>
>      sk_tx_queue_clear(sk);
>      sk->sk_dst_pending_confirm = 0;
>      old_dst = rcu_dereference_protected(sk->sk_dst_cache,
>                          lockdep_sock_is_held(sk));
>      rcu_assign_pointer(sk->sk_dst_cache, dst);
>      dst_release(old_dst);
> }

I am quite familiar with this code.

What are you trying to say exactly ?

Please come with a V2 without grabbing the socket lock.