Re: [BUG] net/ipv4: inconsistent routing table

On Thu, Aug 6, 2015 at 1:45 AM, Alexander Duyck
[off-list ref] wrote:

On 08/05/2015 02:06 AM, Daniel Borkmann wrote:

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[ please cc netdev ]

On 08/05/2015 10:56 AM, Zang MingJie wrote:

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Hi:

I found a bug when remove an ip address which is referenced by a routing
entry.

step to reproduce:

ip li add type dummy
ip li set dummy0 up
ip ad add 10.0.0.1/24 dev dummy0
ip ad add 10.0.0.2/24 dev dummy0

Okay, so up to this point you have 2 addresses on the same subnet that are
now on dummy0.

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ip ro add default via 10.0.0.2/24

This makes the default route go through 10.0.0.2.

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ip ad del 10.0.0.2/24 dev dummy0

Then you remove 10.0.0.2 from the local system, however since 10.0.0.1 is on
the same subnet dummy0 would still be the correct interface to access
10.0.0.2 it is just no longer local to the system.

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after deleting the secondary ip address, the routing entry still
pointing to 10.0.0.2

You didn't delete the default routing entry so why would you expect it to
change?  All you did is remove 10.0.0.2 from the local system.  I believe
the assumption is that 10.0.0.2 is still out there somewhere, it just isn't
on the local system anymore.

Yes, 10.0.0.2 is migrated to somewhere else

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# ip ro
default via 10.0.0.2 dev dummy0
10.0.0.0/24 dev dummy0  proto kernel  scope link  src 10.0.0.1

This matches up with what I would expect.  10.0.0.2 is the default gateway
and it is accessible from dummy0 since 10.0.0.0/24 is accessible from
dummy0.

This means 0.0.0.0/0 is accessible via 10.0.0.2 on the network of dummy0

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but actually, kernel considers the default route is directly connected.

# ip ro get 1.1.1.1
1.1.1.1 dev dummy0  src 10.0.0.1
     cache

I'm not sure how you came to the "directly connected" conclusion. It is
still routing things out through 10.0.0.2 from 10.0.0.1.

Maybe your example would work better if you used 10.0.0.1 and 10.0.1.1
instead.  Then I think you might be able to better see that when you delete
the second address the route would be broken.

No, it isn't. when ping 1.1.1.1, kernel will directly send arp request
braodcast to 1.1.1.1, this is not what I expect. it should send arp
request to 10.0.0.2, following should be the correct routing entry:

# ip ro get 1.1.1.1
1.1.1.1 via 10.0.0.2 dev dummy0  src 10.0.0.1
    cache

- Alex