From: Guillaume Nault gnault@redhat.com
commit 2e5a6266fbb11ae93c468dfecab169aca9c27b43 upstream.
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: 8f97339d3feb ("netfilter: add ipv4 reverse path filter match") Signed-off-by: Guillaume Nault gnault@redhat.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/ipv4/netfilter/ipt_rpfilter.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/netfilter/ipt_rpfilter.c +++ b/net/ipv4/netfilter/ipt_rpfilter.c @@ -76,7 +76,7 @@ static bool rpfilter_mt(const struct sk_ flow.daddr = iph->saddr; flow.saddr = rpfilter_get_saddr(iph->daddr); flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0; - flow.flowi4_tos = RT_TOS(iph->tos); + flow.flowi4_tos = iph->tos & IPTOS_RT_MASK; flow.flowi4_scope = RT_SCOPE_UNIVERSE; flow.flowi4_oif = l3mdev_master_ifindex_rcu(xt_in(par));