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Sat, 28 Nov 2020 09:03:43 -0800 (PST) Subject: Re: [PATCH net] ipv4: Fix tos mask in inet_rtm_getroute() To: Guillaume Nault , David Miller , Jakub Kicinski Cc: netdev@vger.kernel.org, Russell Strong References: From: David Ahern Message-ID: Date: Sat, 28 Nov 2020 10:03:42 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 > --- > net/ipv4/route.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > Reviewed-by: David Ahern