netdev - Re: [PATCH] ipv6: clear RTF_EXPIRES when call ip6_rt

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Message-ID: <20131217083048.GB18396@order.stressinduktion.org>
Date:	Tue, 17 Dec 2013 09:30:48 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Gao feng <gaofeng@...fujitsu.com>
Cc:	RongQing Li <roy.qing.li@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: clear RTF_EXPIRES when call ip6_rt_copy

On Tue, Dec 17, 2013 at 03:46:24PM +0800, Gao feng wrote:
> > Gao, do you still remember why you used RTF_ADDRCONF|RTF_DEFAULT?
> > 
> 
> It's a mystery， I noticed this problem when I wrote the codes.
> http://lists.openwall.net/netdev/2012/03/19/7

I already found this thread, thanks. ;)

> I used the flags RTF_ADDRCONF|RTF_DEFAULT because they are exist in
> rt6_{get,add,purge}_dflt_router.

I thought so, but we have to deal with !DEFAULT ADDRCONF routes, too.

> The from of new cloned rt should not be set if it's impossible for the ort
> to be expired.

Ok.

> but seems we should set from if flags have RTF_ADDRCONF bit. RA package
> not only generate the default route.

Exactly, but it is worse:

Prefix routes can be added with expiration time if user space installs a
prefix with valid_lft != infinity. So I fear we already have permament route
entries which expire.

Userspace router advertisment listener already use that.

I fear the flags don't have a well defined semantic any more. :(

As for the original patch in this thread, I would suggest to hold it
back until this mess is understood. Ok?

Thanks,

  Hannes

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