In short, sctp is likely to incorrectly choose src address if socket is
bound to secondary addresses. This patch fixes it by adding a new check
that checks if such src address belongs to the interface that routing
identified as output.
This is enough to avoid rp_filter drops on remote peer.
Details:
Currently, sctp will do a routing attempt without specifying the src
address and compare the returned value (preferred source) with the
addresses that the socket is bound to. When using secondary addresses,
this will not match.
Then it will try specifying each of the addresses that the socket is
bound to and re-routing, checking if that address is valid as src for
that dst. Thing is, this check alone is weak:
# ip r l
192.168.100.0/24 dev eth1 proto kernel scope link src 192.168.100.149
192.168.122.0/24 dev eth0 proto kernel scope link src 192.168.122.147
# ip a l
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 52:54:00:15:18:6a brd ff:ff:ff:ff:ff:ff
inet 192.168.122.147/24 brd 192.168.122.255 scope global dynamic eth0
valid_lft 2160sec preferred_lft 2160sec
inet 192.168.122.148/24 scope global secondary eth0
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:fe15:186a/64 scope link
valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 52:54:00:b3:91:46 brd ff:ff:ff:ff:ff:ff
inet 192.168.100.149/24 brd 192.168.100.255 scope global dynamic eth1
valid_lft 2162sec preferred_lft 2162sec
inet 192.168.100.148/24 scope global secondary eth1
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:feb3:9146/64 scope link
valid_lft forever preferred_lft forever
4: ens9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 52:54:00:05:47:ee brd ff:ff:ff:ff:ff:ff
inet6 fe80::5054:ff:fe05:47ee/64 scope link
valid_lft forever preferred_lft forever
# ip r g 192.168.100.193 from 192.168.122.148
192.168.100.193 from 192.168.122.148 dev eth1
cache
Even if you specify an interface:
# ip r g 192.168.100.193 from 192.168.122.148 oif eth1
192.168.100.193 from 192.168.122.148 dev eth1
cache
Although this would be valid, peers using rp_filter will drop such
packets as their src doesn't match the routes for that interface.
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
0ca50d12fe