* [PATCH net] ipv4: Ignore ECN bits for fib lookups in fib_compute_spec_dst()
@ 2020-12-24 19:01 Guillaume Nault
2020-12-28 22:45 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Guillaume Nault @ 2020-12-24 19:01 UTC (permalink / raw)
To: David Miller, Jakub Kicinski; +Cc: netdev
RT_TOS() only clears one of the ECN bits. Therefore, when
fib_compute_spec_dst() resorts to a fib lookup, it can return
different results depending on the value of the second ECN bit.
For example, ECT(0) and ECT(1) packets could be treated differently.
$ 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 lo up
$ ip -netns ns1 link set dev lo up
$ ip -netns ns0 link set dev veth01 up
$ ip -netns ns1 link set dev veth10 up
$ ip -netns ns0 address add 192.0.2.10/24 dev veth01
$ ip -netns ns1 address add 192.0.2.11/24 dev veth10
$ ip -netns ns1 address add 192.0.2.21/32 dev lo
$ ip -netns ns1 route add 192.0.2.10/32 tos 4 dev veth10 src 192.0.2.21
$ ip netns exec ns1 sysctl -wq net.ipv4.icmp_echo_ignore_broadcasts=0
With TOS 4 and ECT(1), ns1 replies using source address 192.0.2.21
(ping uses -Q to set all TOS and ECN bits):
$ ip netns exec ns0 ping -c 1 -b -Q 5 192.0.2.255
[...]
64 bytes from 192.0.2.21: icmp_seq=1 ttl=64 time=0.544 ms
But with TOS 4 and ECT(0), ns1 replies using source address 192.0.2.11
because the "tos 4" route isn't matched:
$ ip netns exec ns0 ping -c 1 -b -Q 6 192.0.2.255
[...]
64 bytes from 192.0.2.11: icmp_seq=1 ttl=64 time=0.597 ms
After this patch the ECN bits don't affect the result anymore:
$ ip netns exec ns0 ping -c 1 -b -Q 6 192.0.2.255
[...]
64 bytes from 192.0.2.21: icmp_seq=1 ttl=64 time=0.591 ms
Fixes: 35ebf65e851c ("ipv4: Create and use fib_compute_spec_dst() helper.")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
---
net/ipv4/fib_frontend.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index cdf6ec5aa45d..84bb707bd88d 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -292,7 +292,7 @@ __be32 fib_compute_spec_dst(struct sk_buff *skb)
.flowi4_iif = LOOPBACK_IFINDEX,
.flowi4_oif = l3mdev_master_ifindex_rcu(dev),
.daddr = ip_hdr(skb)->saddr,
- .flowi4_tos = RT_TOS(ip_hdr(skb)->tos),
+ .flowi4_tos = ip_hdr(skb)->tos & IPTOS_RT_MASK,
.flowi4_scope = scope,
.flowi4_mark = vmark ? skb->mark : 0,
};
--
2.21.3
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH net] ipv4: Ignore ECN bits for fib lookups in fib_compute_spec_dst()
2020-12-24 19:01 [PATCH net] ipv4: Ignore ECN bits for fib lookups in fib_compute_spec_dst() Guillaume Nault
@ 2020-12-28 22:45 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2020-12-28 22:45 UTC (permalink / raw)
To: gnault; +Cc: kuba, netdev
From: Guillaume Nault <gnault@redhat.com>
Date: Thu, 24 Dec 2020 20:01:09 +0100
> RT_TOS() only clears one of the ECN bits. Therefore, when
> fib_compute_spec_dst() resorts to a fib lookup, it can return
> different results depending on the value of the second ECN bit.
>
> For example, ECT(0) and ECT(1) packets could be treated differently.
>
> $ 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 lo up
> $ ip -netns ns1 link set dev lo up
> $ ip -netns ns0 link set dev veth01 up
> $ ip -netns ns1 link set dev veth10 up
>
> $ ip -netns ns0 address add 192.0.2.10/24 dev veth01
> $ ip -netns ns1 address add 192.0.2.11/24 dev veth10
>
> $ ip -netns ns1 address add 192.0.2.21/32 dev lo
> $ ip -netns ns1 route add 192.0.2.10/32 tos 4 dev veth10 src 192.0.2.21
> $ ip netns exec ns1 sysctl -wq net.ipv4.icmp_echo_ignore_broadcasts=0
>
> With TOS 4 and ECT(1), ns1 replies using source address 192.0.2.21
> (ping uses -Q to set all TOS and ECN bits):
>
> $ ip netns exec ns0 ping -c 1 -b -Q 5 192.0.2.255
> [...]
> 64 bytes from 192.0.2.21: icmp_seq=1 ttl=64 time=0.544 ms
>
> But with TOS 4 and ECT(0), ns1 replies using source address 192.0.2.11
> because the "tos 4" route isn't matched:
>
> $ ip netns exec ns0 ping -c 1 -b -Q 6 192.0.2.255
> [...]
> 64 bytes from 192.0.2.11: icmp_seq=1 ttl=64 time=0.597 ms
>
> After this patch the ECN bits don't affect the result anymore:
>
> $ ip netns exec ns0 ping -c 1 -b -Q 6 192.0.2.255
> [...]
> 64 bytes from 192.0.2.21: icmp_seq=1 ttl=64 time=0.591 ms
>
> Fixes: 35ebf65e851c ("ipv4: Create and use fib_compute_spec_dst() helper.")
> Signed-off-by: Guillaume Nault <gnault@redhat.com>
Applied and queued up for -stable, thanks.
^ permalink raw reply [flat|nested] 2+ messages in thread
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