linux-kernel - Re: [PATCH] net: Add default_advmss() methods to blackhole dst

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Date:	Fri, 18 Feb 2011 21:16:42 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	George Spelvin <linux@...izon.com>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Roland Dreier <roland@...estorage.com>
Subject: Re: [PATCH] net: Add default_advmss() methods to blackhole dst_ops

On Fri, Feb 18, 2011 at 5:57 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
> I suspect following patch is needed
>
> CC Roland Dreier <roland@...estorage.com> because he fixed the
> default_mtu problem in commit ec831ea72ee5d7d47
> (net: Add default_mtu() methods to blackhole dst_ops)
>
> Thanks !
>
> [PATCH] net: Add default_advmss() methods to blackhole dst_ops
>
> Commit 0dbaee3b37e118a (net: Abstract default ADVMSS behind an
> accessor.) introduced a possible crash in tcp_connect_init(), when
> dst->default_advmss() is called from dst_metric_advmss()
>
> Reported-by: George Spelvin <linux@...izon.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> CC: Roland Dreier <roland@...estorage.com>
> ---
>  net/ipv4/route.c |    7 +++++++
>  net/ipv6/route.c |    6 ++++++
>  2 files changed, 13 insertions(+)
>
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index 788a3e7..5edb605 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -2712,6 +2712,12 @@ static unsigned int ipv4_blackhole_default_mtu(const struct dst_entry *dst)
>        return 0;
>  }
>
> +static unsigned int ipv4_blackhole_default_advmss(const struct dst_entry *dst)
> +{
> +       return 256;
> +}
> +
> +

I am wondering why magic number 256 is used here. Is there a special
reason? Thanks.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
--
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