From: "David S. Miller" <davem@davemloft.net>
To: Thomas Graf <tgraf@suug.ch>
Cc: herbert@gondor.apana.org.au, kuznet@ms2.inr.ac.ru, netdev@oss.sgi.com
Subject: Re: [PATCH] NETLINK: Use SKB_MAXORDER to calculate NLMSG_GOODSIZE
Date: Sun, 6 Feb 2005 22:27:12 -0800 [thread overview]
Message-ID: <20050206222712.5519bc22.davem@davemloft.net> (raw)
In-Reply-To: <20050128234022.GW31837@postel.suug.ch>
On Sat, 29 Jan 2005 00:40:22 +0100
Thomas Graf <tgraf@suug.ch> wrote:
> > > Using SKB_MAXORDER solves this potential leak at the cost of
> > > slightly smaller but safer sizes for some architectures.
> >
> > At first glance it's not clear which of sk_buff or skb_shared_info
> > is bigger. So it might even end up being bigger :)
>
> skb_shared_info is 160 bytes and sk_buff is 196 bytes on my box (x86)
> but that's not the point. We need to take SMP_CACHE_BYTES alignment into
> account which tends to be quite big. The original NLMSG_GOODSIZE
> results in 3908 on my box and gets pumped up to 4128 by skb_alloc
> (ALIGN(...,SMP_CACHE_BYTES) + sizeof(struct skb_shared_info)) having
> SMP_CACHE_BYTES at 128.
Furthermore, it's not sk_buff that's ever the issue. The SKB data
area size is where the skb_shared_info gets tacked onto, sk_buff's
size is never added to this calculation.
next prev parent reply other threads:[~2005-02-07 6:27 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-28 23:03 [PATCH] NETLINK: Use SKB_MAXORDER to calculate NLMSG_GOODSIZE Thomas Graf
2005-01-28 23:22 ` Herbert Xu
2005-01-28 23:40 ` Thomas Graf
2005-02-07 6:27 ` David S. Miller [this message]
2005-01-28 23:48 ` Alexey Kuznetsov
2005-01-29 0:21 ` Thomas Graf
2005-01-29 0:27 ` Thomas Graf
2005-02-07 6:32 ` David S. Miller
2005-02-07 13:28 ` Thomas Graf
2005-02-07 14:27 ` [PATCH] NET: Fix calculation for collapsed skb size Thomas Graf
2005-02-09 4:54 ` David S. Miller
2005-01-29 18:40 ` [PATCH] NETLINK: Use SKB_MAXORDER to calculate NLMSG_GOODSIZE Alexey Kuznetsov
2005-01-29 12:47 ` Thomas Graf
2005-02-06 18:54 ` Thomas Graf
2005-02-06 21:08 ` David S. Miller
2005-02-07 6:25 ` David S. Miller
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