netdev - Re: [RFC][PATCH] Fixing SA/SP dumps on netlink/af

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Date:	Thu, 17 Jan 2008 12:01:17 +0200
From:	Timo Teräs <timo.teras@....fi>
To:	David Miller <davem@...emloft.net>
CC:	herbert@...dor.apana.org.au, hadi@...erus.ca,
	netdev@...r.kernel.org
Subject: Re: [RFC][PATCH] Fixing SA/SP dumps on netlink/af_key

David Miller wrote:
> From: Timo_Teräs <timo.teras@....fi>
> Date: Thu, 17 Jan 2008 11:38:13 +0200
> 
>> The af_key issue is that in big dumps you get only first X
>> entries. The rest of the entries are dropped because the
>> socket receive buffer goes full. You get data corruption:
>> missing entries.
> 
> This is an inherent aspect of AF_KEY (and what it was
> derived from, BSD routing sockets).

Yes, this is the way BSD does it.
 
> It has to provide dumps atomically, and if there is no
> space there is no way to provide those entries which
> would require more rcvbuf space.

RFC does not say it has to be atomic.

It does say that the dump is terminated with SADB_DUMP
message having sadb_seq field set to zero. Currently
that is dropped too when the problem occurs. Thus the
socket is left in a bad state: dump ends never. This
can cause applications without any workarounds to hang.

- Timo
 
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