[BUG] Iproute2 batch-mode fails to bring up veth

Hey all,

Sorry if this isn't the right place to report Iproute2 bugs. It was implied by README.devel as well as a couple of entries I saw in bugzilla.

I use iproute2 batch mode to construct network namespaces. Example script:

   $ cat ~/bin/netns-test.sh
   #! /bin/bash

   gw=192.168.5.1
   ip=192.168.5.2
   ns=netns-test
   veth0=${ns}-0
   veth1=${ns}-1

   /usr/local/sbin/ip -b - << EOF
   link add $veth0 type veth peer name $veth1
   addr add $gw peer $ip dev $veth0
   link set dev $veth0 up
   netns add $ns
   link set $veth1 netns $ns
   netns exec $ns ip link set dev lo up
   netns exec $ns ip link set dev $veth1 up
   netns exec $ns ip addr add $ip/24 dev $veth1
   netns exec $ns ip addr add $ip peer $gw dev $veth1
   netns exec $ns ip route add default via $gw dev $veth1
   netns exec $ns ip route add 192.168.0.0/24 via $gw dev $veth1
   EOF


I noticed when version 5.11.0 dropped that this stops working. Batch mode fails to bring up the inner veth.

Expected usage (as produced by v5.10.0):

   $ sudo ./bin/netns-test.sh
   $ sudo ip netns exec netns-test ip route
   default via 192.168.5.1 dev netns-test-1
   192.168.0.0/24 via 192.168.5.1 dev netns-test-1
   192.168.5.0/24 dev netns-test-1 proto kernel scope link src 192.168.5.2
   192.168.5.1 dev netns-test-1 proto kernel scope link src 192.168.5.2

Actual behaviour:

   $ sudo ./bin/netns-test.sh
   $ sudo ip netns exec netns-test ip route  # Notice the empty output
   $ sudo ip netns exec netns-test ip link
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
       link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
   39: netns-test-1@if40: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
       link/ether 1a:96:4e:4f:84:31 brd ff:ff:ff:ff:ff:ff link-netnsid 0

System info:

* Distro: Void Linux
* Kernel version: 5.10.23
* CPU: AMD Ryzen 7 1800X and Ryzen 5 2600. (Reproduced on both.)

Git bisect pinpoints this commit: https://github.com/shemminger/iproute2/commit/1d9a81b8c9f30f9f4abeb875998262f61bf10577

That commit was focused on refactoring batch mode. This is consistent with my experience that only batch mode is affected. Everything works as expected when running the commands manually.

~ Tim