netdev - [PATCH iproute2] ip route: broken logic when using default word and family not specified

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Message-ID: <CABXn0zdkK4fgHKuDn2a27BoPFDas-vcS9eTRiZsmxadsqaRHxA@mail.gmail.com>
Date:   Sat, 18 Nov 2017 14:12:48 +0100
From:   Alexander Zubkov <zubkov318@...il.com>
To:     netdev@...r.kernel.org
Subject: [PATCH iproute2] ip route: broken logic when using default word and
 family not specified

Hello,

I have found odd behaviour when using "ip route list" (and other bound
commands) with prefix "default".

When family not specified, its value is completely ignored and "ip
route list default" shows all inet4 prefixes. Same do "ip route list
exact default" and "ip route list match default". Examples are at the
end of the message.

When family is specified, the behaviour changes and default works as
expected (=0.0.0.0/0 for inet4 and =::/0 for inet6). The above
commands all shows only default prefix in the output and only "root
default" shows all prefixes.

I tried to dig into the code and found that when default is using with
unspecified family - the resulting structures filter.[mr]dst will
actually become all-zeroes as in the case when nothing is specified.

I propose to change this in such a way (see attached patch). When
default prefix is parsed, the flag PREFIXLEN_SPECIFIED is attached to
it too, like for prefixes with "/<masklen>". It seems logical to me,
because "/0" is really implied by "default" and even directly set up
in the code:

dst->bitlen = 0;

Then during filtering there is additional logic for unspecified family
and specified prefix.

With this patch ip route list commands shown above are working as
expected. And it also works with unspecified table when routes are
printed from different families.

Examples after applying the patch:

# ./ip route list
default via 192.168.0.2 dev eth0
192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.1
192.168.1.0/24 via 192.168.0.3 dev eth0
# ./ip -6 route list
fe80::/64 dev eth0 proto kernel metric 256 pref medium
fe80:1::/64 via fe80::3 dev eth0 metric 1024 pref medium
default via fe80::2 dev eth0 metric 1024 pref medium
# ./ip route list default
default via 192.168.0.2 dev eth0
# ./ip route list exact default
default via 192.168.0.2 dev eth0
# ./ip route list match default
default via 192.168.0.2 dev eth0
# ./ip route list root default
default via 192.168.0.2 dev eth0
192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.1
192.168.1.0/24 via 192.168.0.3 dev eth0
# ./ip route list default table all
default via 192.168.0.2 dev eth0
unreachable default dev lo proto kernel metric 4294967295 error -101 pref medium
default via fe80::2 dev eth0 metric 1024 pref medium
unreachable default dev lo proto kernel metric 4294967295 error -101 pref medium
unreachable default dev lo proto kernel metric 4294967295 error -101 pref medium
# ./ip route list root default table all
default via 192.168.0.2 dev eth0
192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.1
...
ff00::/8 dev eth0 table local metric 256 pref medium
unreachable default dev lo proto kernel metric 4294967295 error -101 pref medium

And before patch:

# ip route list default
default via 192.168.0.2 dev eth0
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.1
192.168.1.0/24 via 192.168.0.3 dev eth0
# ip route list match default
default via 192.168.0.2 dev eth0
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.1
192.168.1.0/24 via 192.168.0.3 dev eth0
# ip route list exact default
default via 192.168.0.2 dev eth0
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.1
192.168.1.0/24 via 192.168.0.3 dev eth0
# ip -4 route list exact default
default via 192.168.0.2 dev eth0
# ip -6 route list exact default
default via fe80::2 dev eth0  metric 1024
# ip route list exact default table all
default via 192.168.0.2 dev eth0
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.1
...
local fe80::3c09:19ff:feee:9866 dev lo  table local  proto none  metric 0
ff00::/8 dev eth0  table local  metric 256
unreachable default dev lo  table unspec  proto kernel  metric
4294967295  error -101

View attachment "list-default.patch" of type "text/x-patch" (3775 bytes)