Re: [Patch net v3 1/2] fib: relax source validation check for loopback packets

[David Ahern <dsahern@gmail.com>]

On 7/17/19 3:41 PM, Cong Wang wrote:
> In a rare case where we redirect local packets from veth to lo,
> these packets fail to pass the source validation when rp_filter
> is turned on, as the tracing shows:
> 
>   <...>-311708 [040] ..s1 7951180.957825: fib_table_lookup: table 254 oif 0 iif 1 src 10.53.180.130 dst 10.53.180.130 tos 0 scope 0 flags 0
>   <...>-311708 [040] ..s1 7951180.957826: fib_table_lookup_nh: nexthop dev eth0 oif 4 src 10.53.180.130
> 
> So, the fib table lookup returns eth0 as the nexthop even though
> the packets are local and should be routed to loopback nonetheless,
> but they can't pass the dev match check in fib_info_nh_uses_dev()
> without this patch.
> 
> It should be safe to relax this check for this special case, as
> normally packets coming out of loopback device still have skb_dst
> so they won't even hit this slow path.
> 
> Cc: Julian Anastasov <ja@ssi.bg>
> Cc: David Ahern <dsahern@gmail.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>  net/ipv4/fib_frontend.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 

Seems ok to me.
Reviewed-by: David Ahern <dsahern@gmail.com>