netdev - Re: [PATCH net] ipv6: tcp: drop silly ICMPv6 packet too big messages

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Date:   Wed, 7 Jul 2021 15:25:55 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>
CC:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Maciej Żenczykowski <maze@...gle.com>
Subject: Re: [PATCH net] ipv6: tcp: drop silly ICMPv6 packet too big messages

On Wed, Jul 07, 2021 at 08:46:30AM -0700, Eric Dumazet wrote:
[ ... ]

> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 593c32fe57ed13a218492fd6056f2593e601ec79..bc334a6f24992c7b5b2c415eab4b6cf51bf36cb4 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -348,11 +348,20 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
>  static void tcp_v6_mtu_reduced(struct sock *sk)
>  {
>  	struct dst_entry *dst;
> +	u32 mtu;
>  
>  	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
>  		return;
>  
> -	dst = inet6_csk_update_pmtu(sk, READ_ONCE(tcp_sk(sk)->mtu_info));
> +	mtu = READ_ONCE(tcp_sk(sk)->mtu_info);
> +
> +	/* Drop requests trying to increase our current mss.
> +	 * Check done in __ip6_rt_update_pmtu() is too late.
> +	 */
> +	if (tcp_mss_to_mtu(sk, mtu) >= tcp_sk(sk)->mss_cache)
Instead of tcp_mss_to_mtu, should this be calling tcp_mtu_to_mss to
compare with tcp_sk(sk)->mss_cache?