netdev - Re: [Patch net] ipv4: fib: check forwarding before checking send

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Date:	Tue, 08 Apr 2014 16:43:56 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	xiyou.wangcong@...il.com
Cc:	netdev@...r.kernel.org, ebiederm@...ssion.com, ja@....bg,
	cwang@...pensource.com
Subject: Re: [Patch net] ipv4: fib: check forwarding before checking
 send_redirects

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Tue,  8 Apr 2014 12:31:22 -0700

> From: Cong Wang <cwang@...pensource.com>
> 
> We have seen in a weird case we had to disable send_redirects in order
> to pass rp filter check even though we don't set forwarding at all.
> This looks wrong, at least according to ip-sysctl.txt send_redirects should
> only make sense when we enable forwarding.
> 
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Julian Anastasov <ja@....bg>
> Cc: David S. Miller <davem@...emloft.net>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> Signed-off-by: Cong Wang <cwang@...pensource.com>

I'm not so sure about this.

This test here is just an optimization, which bypasses the long path
processing of FIB source address validation if certain strict
conditions are met.

__fib_validate_source() should do the right thing if it is executed,
it is just the slow path, and you should determine why it is rejecting
your traffic instead.

Your change is a valid optimization perhaps, but not a bug fix.
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