netdev - Re: [PATCHv3 net] ipv6: do not match device when remove source route

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Date: Wed, 26 Jul 2023 17:46:03 +0800
From: Hangbin Liu <liuhangbin@...il.com>
To: David Ahern <dsahern@...nel.org>
Cc: Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Thomas Haller <thaller@...hat.com>,
	Donald Sharp <sharpd@...dia.com>
Subject: Re: [PATCHv3 net] ipv6: do not match device when remove source route

On Tue, Jul 25, 2023 at 04:37:15PM -0600, David Ahern wrote:
> > This already happens in IPv4:
> > 
> > # ip link add name dummy1 up type dummy
> > # ip link add name dummy2 up type dummy
> > # ip address add 192.0.2.1/24 dev dummy1
> > # ip route add 198.51.100.0/24 dev dummy2 src 192.0.2.1
> > # ip -4 r s
> > 192.0.2.0/24 dev dummy1 proto kernel scope link src 192.0.2.1 
> > 198.51.100.0/24 dev dummy2 scope link src 192.0.2.1 
> > # ip address del 192.0.2.1/24 dev dummy1
> > # ip -4 r s
> > 
> > IPv6 only removes the preferred source address from routes, but doesn't
> > delete them. The patch doesn't change that.
> > 
> > Another difference from IPv4 is that IPv6 only removes the preferred
> > source address from routes whose first nexthop device matches the device
> > from which the address was removed:
> > 
> > # ip link add name dummy1 up type dummy
> > # ip link add name dummy2 up type dummy
> > # ip address add 2001:db8:1::1/64 dev dummy1
> > # ip route add 2001:db8:2::/64 dev dummy2 src 2001:db8:1::1
> > # ip -6 r s
> > 2001:db8:1::/64 dev dummy1 proto kernel metric 256 pref medium
> > 2001:db8:2::/64 dev dummy2 src 2001:db8:1::1 metric 1024 pref medium
> > fe80::/64 dev dummy1 proto kernel metric 256 pref medium
> > fe80::/64 dev dummy2 proto kernel metric 256 pref medium
> > # ip address del 2001:db8:1::1/64 dev dummy1
> > # ip -6 r s
> > 2001:db8:2::/64 dev dummy2 src 2001:db8:1::1 metric 1024 pref medium
> > fe80::/64 dev dummy1 proto kernel metric 256 pref medium
> > fe80::/64 dev dummy2 proto kernel metric 256 pref medium
> > 
> > And this is despite the fact that the kernel only allowed the route to
> > be programmed because the preferred source address was present on
> > another interface in the same L3 domain / VRF:
> > 
> > # ip link add name dummy1 up type dummy
> > # ip link add name dummy2 up type dummy
> > # ip route add 2001:db8:2::/64 dev dummy2 src 2001:db8:1::1
> > Error: Invalid source address.
> > 
> > The intent of the patch (at least with the changes I proposed) is to
> > remove the preferred source address from routes in a VRF when the
> > address is no longer configured on any interface in the VRF.
> > 
> > Note that the above is true for addresses with a global scope. The
> > removal of a link-local address from a device should not affect other
> > devices. This restriction also applies when a route is added:
> > 
> > # ip link add name dummy1 up type dummy
> > # ip link add name dummy2 up type dummy
> > # ip -6 address add fe80::1/64 dev dummy1
> > # ip -6 route add 2001:db8:2::/64 dev dummy2 src fe80::1
> > Error: Invalid source address.
> > # ip -6 address add fe80::1/64 dev dummy2
> > # ip -6 route add 2001:db8:2::/64 dev dummy2 src fe80::1
> 
> Lot of permutations. It would be good to get these in a test script
> along with other variations - e.g.,
> 
> # 2 devices with the same source address
> ip link add name dummy1 up type dummy
> ip link add name dummy2 up type dummy
> ip link add name dummy3 up type dummy
> ip address add 192.0.2.1/24 dev dummy1
> ip address add 192.0.2.1/24 dev dummy3
> ip route add 198.51.100.0/24 dev dummy2 src 192.0.2.1
> ip address del 192.0.2.1/24 dev dummy1
> --> src route should stay
> 
> # VRF with single device using src address
> ip li add name red up type vrf table 123
> ip link add name dummy4 up type dummy vrf red
> ip link add name dummy5 up type dummy vrf red
> ip address add 192.0.2.1/24 dev dummy4
> ip route add 198.51.100.0/24 dev dummy5 src 192.0.2.1
> ip address del 192.0.2.1/24 dev dummy4
> ip ro ls vrf red
> 
> # VRF with two devices using src address
> ip li add name red up type vrf table 123
> ip link add name dummy4 up vrf red type dummy
> ip link add name dummy5 up vrf red type dummy
> ip link add name dummy6 up vrf red type dummy
> ip address add 192.0.2.1/24 dev dummy4
> ip address add 192.0.2.1/24 dev dummy6
> ip route add 198.51.100.0/24 dev dummy5 src 192.0.2.1 vrf red
> ip address del 192.0.2.1/24 dev dummy4

I can add these to fib_tests later.

Hangbin