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Date:	Mon, 15 Oct 2007 18:43:06 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Satoshi OSHIMA <satoshi.oshima.fk@...achi.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Hideo AOKI <hideo.aoki.tk@...achi.com>,
	Yumiko SUGITA <yumiko.sugita.yf@...achi.com>,
	"青木@RedHat" <haoki@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	吉藤 英明 <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH 4/4] UDP memory accounting and limitation(take 5): memory limitation

On Fri, Oct 12, 2007 at 09:11:27PM +0900, Satoshi OSHIMA wrote:
>
> +static inline int __ip_check_max_skb_pages(struct sock *sk, int size)
> +{
> +	switch(sk->sk_protocol) {
> +	case IPPROTO_UDP:
> +		if (sk->sk_prot->sysctl_mem[0] > UDP_MIN_SKB_PAGES)
> +			if (atomic_read(sk->sk_prot->memory_allocated)+size
> +			    >= sk->sk_prot->sysctl_mem[0])
> +				return -ENOBUFS;
> +		/* Fall through */	
> +	default:
> +		break;
> +	}
> +	return 0;
> +}

Since you're not doing a per-user limit, you must give each
socket a minimum even when the total exceeds your threshold.

Otherwise any local user can trivially DoS the whole system.

> +UDP variables:
> +
> +udp_mem - INTERGER
> +	Number of pages allowed for queueing by all UDP sockets.
> +	Minimal value is 4096. If 4096 is set, UDP memory will not
> +	be limited.
> +	Default: 4096

This seems to be a rather confusing setup.  We don't set a
minimum for TCP so is this really necessary?

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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