On Sat, 28 Nov 2020 10:03:42 -0700 David Ahern wrote:
> On 11/26/20 11:09 AM, Guillaume Nault wrote:
> > When inet_rtm_getroute() was converted to use the RCU variants of
> > ip_route_input() and ip_route_output_key(), the TOS parameters
> > stopped being masked with IPTOS_RT_MASK before doing the route lookup.
> >
> > As a result, "ip route get" can return a different route than what
> > would be used when sending real packets.
> >
> > For example:
> >
> > $ ip route add 192.0.2.11/32 dev eth0
> > $ ip route add unreachable 192.0.2.11/32 tos 2
> > $ ip route get 192.0.2.11 tos 2
> > RTNETLINK answers: No route to host
> >
> > But, packets with TOS 2 (ECT(0) if interpreted as an ECN bit) would
> > actually be routed using the first route:
> >
> > $ ping -c 1 -Q 2 192.0.2.11
> > PING 192.0.2.11 (192.0.2.11) 56(84) bytes of data.
> > 64 bytes from 192.0.2.11: icmp_seq=1 ttl=64 time=0.173 ms
> >
> > --- 192.0.2.11 ping statistics ---
> > 1 packets transmitted, 1 received, 0% packet loss, time 0ms
> > rtt min/avg/max/mdev = 0.173/0.173/0.173/0.000 ms
> >
> > This patch re-applies IPTOS_RT_MASK in inet_rtm_getroute(), to
> > return results consistent with real route lookups.
> >
> > Fixes: 3765d35ed8b9 ("net: ipv4: Convert inet_rtm_getroute to rcu versions
> > of route lookup")
> > Signed-off-by: Guillaume Nault <[email protected]>
>
> Reviewed-by: David Ahern <[email protected]>
Applied, thanks!
Should the discrepancy between the behavior of ip_route_input_rcu() and
ip_route_input() be addressed, possibly?
