diff options
| author | Guillaume Nault <gnault@redhat.com> | 2021-01-16 11:44:22 +0100 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2021-01-19 13:54:30 -0800 |
| commit | 8d2b51b008c25240914984208b2ced57d1dd25a5 (patch) | |
| tree | 4383cf77e4e5a9c9a0d78cf5a1c1fe195e5d771f /net | |
| parent | f7b9820dbe1620a3d681991fc82774ae49c2b6d2 (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.c | 3 |
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; |