OpenWrt/LEDE Project

  • Status Closed
  • Percent Complete
  • Task Type Bug Report
  • Category Base system
  • Assigned To No-one
  • Operating System All
  • Severity Critical
  • Priority Very Low
  • Reported Version Trunk
  • Due in Version Undecided
  • Due Date Undecided
  • Votes 2
  • Private
Attached to Project: OpenWrt/LEDE Project
Opened by nouman8 - 19.10.2017
Last edited by Koen Vandeputte - 05.10.2018

FS#1083 - ar71xx Kernel 4.9 PPTP Passthrough not working

today i compiled for my TP-Link mr3420 v2 with Kerenl 4.9 by simply changing the KERNEL_PATCHVER:=4.4 to KERNEL_PATCHVER:=4.9 in target/linux/ar71xx/Makefile , everything works good so far except i am not able to connect to the VPN which was working good previously with 4.4 kernel compiled lede a week back.

Closed by  Koen Vandeputte
05.10.2018 07:44
Reason for closing:  Not a bug
chandlerding commented on 21.10.2017 16:44

Install kmod-nf-nathelper-extra and try again?

nouman8 commented on 23.10.2017 03:04

kmod-nf-nathelper-extra is installed

nouman8 commented on 25.10.2017 12:28

if anyone else could test this behavior on their ar71xx device with 4.9 kernel ??

Martin Bouska commented on 02.12.2017 14:55

yes, me.
Way to reproduce:
1. flash the Reboot development snapshot image External Linklede-ar71xx-generic-tl-mr3420-v2-squashfs-sysupgrade.bin
2. opkg install kmod-nf-nathelper-extra
3. try the PPTP connection from LAN to external host without succes

I have tried to compile the image from trunk sources, then tried the image generator, but it is always the same:

the module nf_nat_pptp is loaded, but not working with 4.9.65 kernel

I found that in kernel logs this message appeared:
"nf_conntrack: default automatic helper assignment has been turned off for security reasons and CT-based firewall rule not found. Use the iptables CT target to attach helpers instead." Im not sure, if it is relevant to this issue - maybe not.

I attached some more detailed infos to this post. If You need some other traces to investigate, dont hasitate to contact me.


Martin Bouska commented on 02.12.2017 20:52

And I confirm, that after building image from trunk source with KERNEL_PATCHVER:=4.4 the problem disappeared.
pptp works fine with older kernel All other options in .config remains same as it was before with 4.9 kernel.

Arjen de Korte commented on 02.12.2017 21:22

This is not surprising. The default for automatic loading of connection tracking helpers was changed in kernel-4.7. So with kernel-4.4, the pptp helper will be loaded automatically when PPTP traffic is seen, but for kernel-4.9 you'll have to do that explicitly.

Adding something along the lines

  iptables -t raw -A OUTPUT -p tcp -m tcp --dport 1723 -j CT --helper pptp

should load the connection tracker helper in your firewall. You could append this line to your /etc/firewall.user for instance to load it automatically.

Martin Bouska commented on 04.12.2017 11:33

Hello and thank You for clearing it out!
After days of trying it to work, finally got an answer.

I decided to keep the older kernel and wait some additional time before updating to 4.9, until all these issues with conntrack helpers will be tested, better documented and user-friendly handled.

I understand, that the automatic loading could be a security issue.
BUT not 100% of the users are iptables config aware, so IMHO is this not the right way to getting it work.
Before it was enough to install the kmod-nf-nathelper-extra and all kinds of traffic passed through like charm.
But now Im not sure, if I can yet determine all of the helpers, wich will be needed in future, in order to add them manually to the .config . It is probably not secure to enable all of them yet (?); and after 1-2 years I will not rememeber how to do it, or even determine that I need to do it.

P.S.: IMHO solution to achieve better security but keep the user friendly management could be splitting the nathelpers-extra into more specific nathelper-pptp , nathelper-sip, etc and add the iptables record automatically within installation without forcing users to do it manually. OR make Luci capable to handle the conntrack config.


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