| From foo@baz Sun Jan 10 02:09:05 PM CET 2021 |
| From: Guillaume Nault <gnault@redhat.com> |
| Date: Thu, 24 Dec 2020 20:01:09 +0100 |
| Subject: ipv4: Ignore ECN bits for fib lookups in fib_compute_spec_dst() |
| |
| From: Guillaume Nault <gnault@redhat.com> |
| |
| [ Upstream commit 21fdca22eb7df2a1e194b8adb812ce370748b733 ] |
| |
| 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> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| net/ipv4/fib_frontend.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/net/ipv4/fib_frontend.c |
| +++ b/net/ipv4/fib_frontend.c |
| @@ -299,7 +299,7 @@ __be32 fib_compute_spec_dst(struct sk_bu |
| .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, |
| }; |