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 <gna...@redhat.com>
> ---
> net/ipv4/route.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
Reviewed-by: David Ahern <dsah...@kernel.org>
