Hello,
On Thu, 7 Apr 2016, Chris Friesen wrote:
> Hi,
>
> We think we may have found a bug in the handling of ipv4 route caching,
> and are curious what you think.
>
> 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.
So, if we store some orig_oif in rt_iif that
is specific (cached in nexthop) to some device, this
orig_oif should match the device. The only case when
this is violated is when we redirect traffic to lo.
Any attempts to store eth1 in rt_iif for nexthop
cache for lo should be avoided.
> 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.
>
> For what it's worth, here's a patch that we've applied locally to deal
> with the issue.
>
> Chris
>
>
>
> Signed-off-by: Allain Legacy <allain.leg...@windriver.com>
> Signed-off-by: Chris Friesen <chris.frie...@windriver.com>
>
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index 02c6229..e965d4b 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -2045,6 +2045,17 @@ 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)) {
So, we can be more specific. Can this work?:
} else if ((type == RTN_LOCAL) && (orig_oif != 0) &&
(orig_oif != dev_out->ifindex)) {
I.e. we should allow to cache orig_oif=LOOPBACK_IFINDEX
but eth1 should not be cached.
> + /* 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 <j...@ssi.bg>
