netdev - Re: [PATCHv3 net-next 3/4] ipv4: shrink current mss for tcp PMTU blackhole detection

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CABrhC0m6nCwHy-CCLiFStYhSbMf78E1i6Lvh=DsPi6Pcg-GCOw@mail.gmail.com>
Date:	Sat, 28 Feb 2015 18:39:58 -0500
From:	John Heffner <johnwheffner@...il.com>
To:	Fan Du <fan.du@...el.com>
Cc:	edumazet@...gle.com, David Miller <davem@...emloft.net>,
	Netdev <netdev@...r.kernel.org>,
	Fan Du <fengyuleidian0615@...il.com>
Subject: Re: [PATCHv3 net-next 3/4] ipv4: shrink current mss for tcp PMTU
 blackhole detection

On Fri, Feb 27, 2015 at 10:23 PM, Fan Du <fan.du@...el.com> wrote:
> Reducing current tcp mss instead of search_low will make
> more sense, as current tcp mss still got lost.

> @@ -113,7 +114,8 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
>                         struct tcp_sock *tp = tcp_sk(sk);
>                         int mss;
>
> -                       mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
> +                       /* try mss smaller than current mss */
> +                       mss = tcp_current_mss(sk) >> 1;
>                         mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
>                         mss = max(mss, 68 - tp->tcp_header_len);
>                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
> @@ -176,7 +178,7 @@ static int tcp_write_timeout(struct sock *sk)

I don't believe there's a problem with the code as written.  Modulo
headers, search_low <= mss =< search_high.  This code, on successive
timeouts, widens the search range by adjusting search_low (and mss)
downward.

  -John
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html