netfilter: rpfilter: mask ecn bits before fib lookup
RT_TOS() only masks one of the two ECN bits. Therefore rpfilter_mt() treats Not-ECT or ECT(1) packets in a different way than those with ECT(0) or CE. Reproducer: Create two netns, connected with a veth: $ ip netns add ns0 $ ip netns add ns1 $ ip link add name veth01 netns ns0 type veth peer name veth10 netns ns1 $ ip -netns ns0 link set dev veth01 up $ ip -netns ns1 link set dev veth10 up $ ip -netns ns0 address add 192.0.2.10/32 dev veth01 $ ip -netns ns1 address add 192.0.2.11/32 dev veth10 Add a route to ns1 in ns0: $ ip -netns ns0 route add 192.0.2.11/32 dev veth01 In ns1, only packets with TOS 4 can be routed to ns0: $ ip -netns ns1 route add 192.0.2.10/32 tos 4 dev veth10 Ping from ns0 to ns1 works regardless of the ECN bits, as long as TOS is 4: $ ip netns exec ns0 ping -Q 4 192.0.2.11 # TOS 4, Not-ECT ... 0% packet loss ... $ ip netns exec ns0 ping -Q 5 192.0.2.11 # TOS 4, ECT(1) ... 0% packet loss ... $ ip netns exec ns0 ping -Q 6 192.0.2.11 # TOS 4, ECT(0) ... 0% packet loss ... $ ip netns exec ns0 ping -Q 7 192.0.2.11 # TOS 4, CE ... 0% packet loss ... Now use iptable's rpfilter module in ns1: $ ip netns exec ns1 iptables-legacy -t raw -A PREROUTING -m rpfilter --invert -j DROP Not-ECT and ECT(1) packets still pass: $ ip netns exec ns0 ping -Q 4 192.0.2.11 # TOS 4, Not-ECT ... 0% packet loss ... $ ip netns exec ns0 ping -Q 5 192.0.2.11 # TOS 4, ECT(1) ... 0% packet loss ... But ECT(0) and ECN packets are dropped: $ ip netns exec ns0 ping -Q 6 192.0.2.11 # TOS 4, ECT(0) ... 100% packet loss ... $ ip netns exec ns0 ping -Q 7 192.0.2.11 # TOS 4, CE ... 100% packet loss ... After this patch, rpfilter doesn't drop ECT(0) and CE packets anymore. Fixes: 8f97339d ("netfilter: add ipv4 reverse path filter match") Signed-off-by:Guillaume Nault <gnault@redhat.com> Signed-off-by:
Jakub Kicinski <kuba@kernel.org>
parent
8d2b51b0
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