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authorGuillaume Nault <gnault@redhat.com>2021-01-16 11:44:22 +0100
committerJakub Kicinski <kuba@kernel.org>2021-01-19 13:54:30 -0800
commit8d2b51b008c25240914984208b2ced57d1dd25a5 (patch)
tree4383cf77e4e5a9c9a0d78cf5a1c1fe195e5d771f /net
parentf7b9820dbe1620a3d681991fc82774ae49c2b6d2 (diff)
udp: mask TOS bits in udp_v4_early_demux()
udp_v4_early_demux() is the only function that calls ip_mc_validate_source() with a TOS that hasn't been masked with IPTOS_RT_MASK. This results in different behaviours for incoming multicast UDPv4 packets, depending on if ip_mc_validate_source() is called from the early-demux path (udp_v4_early_demux) or from the regular input path (ip_route_input_noref). ECN would normally not be used with UDP multicast packets, so the practical consequences should be limited on that side. However, IPTOS_RT_MASK is used to also masks the TOS' high order bits, to align with the non-early-demux path behaviour. Reproducer: Setup two netns, connected with veth: $ ip netns add ns0 $ ip netns add ns1 $ ip -netns ns0 link set dev lo up $ ip -netns ns1 link set dev lo up $ 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 peer 192.0.2.11/32 dev veth01 $ ip -netns ns1 address add 192.0.2.11 peer 192.0.2.10/32 dev veth10 In ns0, add route to multicast address 224.0.2.0/24 using source address 198.51.100.10: $ ip -netns ns0 address add 198.51.100.10/32 dev lo $ ip -netns ns0 route add 224.0.2.0/24 dev veth01 src 198.51.100.10 In ns1, define route to 198.51.100.10, only for packets with TOS 4: $ ip -netns ns1 route add 198.51.100.10/32 tos 4 dev veth10 Also activate rp_filter in ns1, so that incoming packets not matching the above route get dropped: $ ip netns exec ns1 sysctl -wq net.ipv4.conf.veth10.rp_filter=1 Now try to receive packets on 224.0.2.11: $ ip netns exec ns1 socat UDP-RECVFROM:1111,ip-add-membership=224.0.2.11:veth10,ignoreeof - In ns0, send packet to 224.0.2.11 with TOS 4 and ECT(0) (that is, tos 6 for socat): $ echo test0 | ip netns exec ns0 socat - UDP-DATAGRAM:224.0.2.11:1111,bind=:1111,tos=6 The "test0" message is properly received by socat in ns1, because early-demux has no cached dst to use, so source address validation is done by ip_route_input_mc(), which receives a TOS that has the ECN bits masked. Now send another packet to 224.0.2.11, still with TOS 4 and ECT(0): $ echo test1 | ip netns exec ns0 socat - UDP-DATAGRAM:224.0.2.11:1111,bind=:1111,tos=6 The "test1" message isn't received by socat in ns1, because, now, early-demux has a cached dst to use and calls ip_mc_validate_source() immediately, without masking the ECN bits. Fixes: bc044e8db796 ("udp: perform source validation for mcast early demux") Signed-off-by: Guillaume Nault <gnault@redhat.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/udp.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 7103b0a89756..69ea76578abb 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2555,7 +2555,8 @@ int udp_v4_early_demux(struct sk_buff *skb)
*/
if (!inet_sk(sk)->inet_daddr && in_dev)
return ip_mc_validate_source(skb, iph->daddr,
- iph->saddr, iph->tos,
+ iph->saddr,
+ iph->tos & IPTOS_RT_MASK,
skb->dev, in_dev, &itag);
}
return 0;