netdev - Re: [PATCH net] netlink: fix netlink

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Message-ID: <20131109000434.GD28793@casper.infradead.org>
Date:	Sat, 9 Nov 2013 00:04:34 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	David Miller <davem@...emloft.net>
Cc:	jbenc@...hat.com, netdev@...r.kernel.org, pablo@...filter.org
Subject: Re: [PATCH net] netlink: fix netlink_ack with large messages

On 11/08/13 at 03:07pm, David Miller wrote:
> From: Jiri Benc <jbenc@...hat.com>
> Date: Thu,  7 Nov 2013 19:57:45 +0100
> 
> > Commit c05cdb1b864f ("netlink: allow large data transfers from user-space")
> > does not handle cases where netlink_ack is used to report an error. In such
> > case, the original message is copied to the ack message, which needs to be
> > large enough.
> > 
> > Signed-off-by: Jiri Benc <jbenc@...hat.com>
> 
> I have two problems with this change.
> 
> First of all, if netlink_ack() has this problem, do not extend the
> netlink_alloc_large_skb() usage to dumps too as your patch is
> doing here.
> 
> Secondly, it seems sort of over the top to quote such enormous
> messages, and in fact wasteful.  We have the sequence number in
> the netlink header, so the user can tell exactly which message
> we are erroring.
> 
> Just quoting such huge requests in ACKs by default doesn't seem
> to make any sense.  I would say that we should have a way to
> turn off the quoting, or at least limit it, and turn this knob
> off for things like nftables that can hit these kinds of cases.

I agree it seems over the top for pure ACKs but we also use
netlink_ack() to report errors where it makes sense to quote
the full message.
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