netdev - Re: skb allocation size question

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Message-ID: <1283367885.2484.16.camel@edumazet-laptop>
Date:	Wed, 01 Sep 2010 21:04:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Aaron Williams <awilliams@...eros.com>
Cc:	netdev@...r.kernel.org
Subject: Re: skb allocation size question

Le mercredi 01 septembre 2010 à 11:51 -0700, Aaron Williams a écrit :
> Hi,
> 
> I have been trying to track down an issue in one of our drivers with SKB 
> allocation and in my research I came across something that seems a bit 
> strange. In __alloc_skb, a block for the data allocates size + sizeof(struct 
> skb_shared_info) bytes, yet skb->truesize is set to size + sizeof(struct 
> sk_buff). Is there a reason for this discrepancy?

Hi Aaron

Not really. We also could add in truesize the sizeof(struct
skb_shared_info).

Including sizeof(struct sk_buff) is enough to prevent a malicious user
filling kernel memory with skb of one byte of payload.

Problem is, adding this extra overhead could slowdown some applications,
using too small RCVBUF / SNDBUF settings.



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