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

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Date:	Wed, 9 Apr 2014 01:03:29 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Cong Wang <xiyou.wangcong@...il.com>
cc:	netdev@...r.kernel.org, davem@...emloft.net,
	Eric Biederman <ebiederm@...ssion.com>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: [Patch net] ipv4: fib: check forwarding before checking
 send_redirects


	Hello,

On Tue, 8 Apr 2014, Cong Wang wrote:

> 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>
> 
> ---
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index 1a629f8..3f9e324 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -321,7 +321,8 @@ int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
>  	int r = secpath_exists(skb) ? 0 : IN_DEV_RPFILTER(idev);
>  
>  	if (!r && !fib_num_tclassid_users(dev_net(dev)) &&
> -	    (dev->ifindex != oif || !IN_DEV_TX_REDIRECTS(idev))) {
> +	    (dev->ifindex != oif || !IN_DEV_FORWARD(idev) ||
> +	     !IN_DEV_TX_REDIRECTS(idev))) {

	Very strange. Above IN_DEV_FORWARD matters only
when dev->ifindex == oif. And this can happen only for the
ip_route_input_slow -> ip_mkroute_input -> __mkroute_input
case. We are not supposed to reach fib_validate_source because
ip_mkroute_input is after the IN_DEV_FORWARD check in
ip_route_input_slow. This was for forwarding.

	If the case is not forwarding but local delivery,
the dev->ifindex != oif condition should be always true
because we provide 0 or LOOPBACK_IFINDEX for oif.

	So, the question is how we reach fib_validate_source
with dev->ifindex == oif and IN_DEV_FORWARD(idev) already
checked to be != 0 ?

>  		*itag = 0;
>  		return 0;
>  	}

Regards

--
Julian Anastasov <ja@....bg>
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