[FS#876] dnsmasq-full "Exclude interfaces" configuration does not work as expected.

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - 7hunderbug (7hunderbug) 

Attached to Project - LEDE Project
Summary - dnsmasq-full "Exclude interfaces" configuration does not work as expected.
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Medium
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Device problem occurs on: BT Home Hub 5A / Lantiq xrx200

Software versions of LEDE release, packages, etc: LEDE Reboot 17.01.2 r3435-65eec8bd5f / LuCI lede-17.01 branch (git-17.163.57307-c79bb96)

Steps to reproduce:

By default, dnsmasq-full listens on all interfaces, including pppoe-wan, tun0, lo, other vpns etc. I want to restrict dnsmasq to listen only on br-lan and lo (I'm also running dns-crypt, wireguard and openvpn) and I want to exclude pppoe-wan, vpn_wg and tun0.

1. Add each interface in a new line under dhcp configuration "Exclude interfaces" and save.
2. SSH to router and check using 'netstat -tulnp' to find that dnsmasq is *still* listening on all interfaces.
3. Examine file /tmp/etc/dnsmasq.conf.cfg02411c to check dnsmasq runtime configuration for multiple "except-interface=" lines. Find that there is only one line showing "except-interface=vpn_wg".

In my attmepts to troubleshoot, I've found that the configuration line "except-interface=" appears for some interfaces only, and only one at a time, otherwise the line is completely absent from the runtime configuration.

I've managed to trace the problem to this commit on github:
 https://github.com/lede-project/source/commit/5cd88f481202dab197e6d7d231b97ecd720d4ded

Reverting this commit on my router fixes the problem and now all interfaces specified for exclusion on the dhcp configuration page are properly ignored and multiple "except-interface=" lines exist in the dnsmasq runtime configuration file.

 

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=876