netdev - Re: [PATCH v4] route: do not cache fib route info on local routes with oif

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Message-ID: <alpine.LFD.2.11.1604090104020.2124@ja.home.ssi.bg>
Date:	Sat, 9 Apr 2016 01:08:17 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Chris Friesen <chris.friesen@...driver.com>
cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v4] route: do not cache fib route info on local routes
 with oif


	Hello,

On Fri, 8 Apr 2016, Chris Friesen wrote:

> For local routes that require a particular output interface we do not want
> to cache the result.  Caching the result causes incorrect behaviour when
> there are multiple source addresses on the interface.  The end result
> being that if the intended recipient is waiting on that interface for the
> packet he won't receive it because it will be delivered on the loopback
> interface and the IP_PKTINFO ipi_ifindex will be set to the loopback
> interface as well.
> 
> This can be tested by running a program such as "dhcp_release" which
> attempts to inject a packet on a particular interface so that it is
> received by another program on the same board.  The receiving process
> should see an IP_PKTINFO ipi_ifndex value of the source interface
> (e.g., eth1) instead of the loopback interface (e.g., lo).  The packet
> will still appear on the loopback interface in tcpdump but the important
> aspect is that the CMSG info is correct.
> 
> Sample dhcp_release command line:
> 
>    dhcp_release eth1 192.168.204.222 02:11:33:22:44:66
> 
> Signed-off-by: Allain Legacy <allain.legacy@...driver.com>
> Signed off-by: Chris Friesen <chris.friesen@...driver.com>

	Looks good to me.

Reviewed-by: Julian Anastasov <ja@....bg>

> ---
>  net/ipv4/route.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index 02c6229..b050cf9 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -2045,6 +2045,18 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
>  		 */
>  		if (fi && res->prefixlen < 4)
>  			fi = NULL;
> +	} else if ((type == RTN_LOCAL) && (orig_oif != 0) &&
> +		   (orig_oif != dev_out->ifindex)) {
> +		/* For local routes that require a particular output interface
> +		 * we do not want to cache the result.  Caching the result
> +		 * causes incorrect behaviour when there are multiple source
> +		 * addresses on the interface, the end result being that if the
> +		 * intended recipient is waiting on that interface for the
> +		 * packet he won't receive it because it will be delivered on
> +		 * the loopback interface and the IP_PKTINFO ipi_ifindex will
> +		 * be set to the loopback interface as well.
> +		 */
> +		fi = NULL;
>  	}
>  
>  	fnhe = NULL;

Regards

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