From: Guillaume Nault <gnault@redhat.com>
To: David Miller <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org, Paolo Abeni <pabeni@redhat.com>
Subject: [PATCH net 1/2] udp: mask TOS bits in udp_v4_early_demux()
Date: Sat, 16 Jan 2021 11:44:22 +0100 [thread overview]
Message-ID: <34f99dc0d1d339a3ee7caa40597ebc8313e4774d.1610790904.git.gnault@redhat.com> (raw)
In-Reply-To: <cover.1610790904.git.gnault@redhat.com>
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>
---
net/ipv4/udp.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
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;
--
2.21.3
next prev parent reply other threads:[~2021-01-16 10:46 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-16 10:44 [PATCH net 0/2] ipv4: Ensure ECN bits don't influence source address validation Guillaume Nault
2021-01-16 10:44 ` Guillaume Nault [this message]
2021-01-16 10:44 ` [PATCH net 2/2] netfilter: rpfilter: mask ecn bits before fib lookup Guillaume Nault
2021-01-19 22:30 ` [PATCH net 0/2] ipv4: Ensure ECN bits don't influence source address validation patchwork-bot+netdevbpf
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