pptp vpn connection, heavily used, completely freezes the computer

Bug #905659 reported by malheum
12
This bug affects 2 people
Affects Status Importance Assigned to Milestone
pptp-linux (Ubuntu)
Confirmed
Undecided
Unassigned

Bug Description

Hello,

I am using a vpn pptp connection to ipredator.se. Heavy use of the pptp completely freezes my computer. Usually the freeze happens within a few minutes. Then both the caps lock and scroll lock led will be blinking. Magic sysrq keys to not work anymore. CTRL-ALT-F1 etc to switch to a terminal window does not work either and the machine does not respond to a ping on the eth0 interface's ip address anymore. In short words: totally and utterly frozen.

I think that the pptp kernel module is not handling the queueing of a larger number of packets correctly (might be interesting if that could be exploited).

Architecture is amd64. The computer is a Dell Latitude D830.

I can reproduce this freeze with the pptp vpn connection running both over the ethernet interface eth0, as well as over the wireless ethernet interface wlan0.

At first I always used the vpn pptp service with network-manager. This is when I first noticed the freezes.

The freezes happen when I heavily use the pptp vpn connection at the airport, hotel or some other hotspot, or when working from a client's site, when I have to access some disk images or larger pdf manuals, or open a couple of tabs at the same moment in firefox, etc.

/var/log/syslog then shows as the last message before the freeze of the machine:
Dec 17 03:12:08 tuxtux pptp[20321]: anon warn[decaps_gre:pptp_gre.c:426]: discarding bogus packet 2650122 (expecting 2648136)
Dec 17 03:12:08 tuxtux pptp[20321]: anon warn[decaps_gre:pptp_gre.c:426]: discarding bogus packet 2650123 (expecting 2648136)
Dec 17 03:12:08 tuxtux pptp[20321]: anon warn[decaps_gre:pptp_gre.c:426]: discarding bogus packet 2650124 (expecting 2648136)
Dec 17 03:12:08 tuxtux pptp[20321]: anon warn[decaps_gre:pptp_gre.c:426]: discarding bogus packet 2650125 (expecting 2648136)
That messages is repeated a couple of hundred times before the syslog entries stops and the machine freezes.

Not being satisfied with a not really working pptp vpn I decided to resort to the beloved command line interface to investigate further.

Configuration needed to reproduce:

/etc/ppp/options.pptp:
lock
noauth
refuse-pap
refuse-eap
refuse-chap
refuse-mschap
nobsdcomp
nodeflate

/etc/ppp/ipredator:
pty "pptp vpn.ipredator.se --nolaunchpppd"
remotename ipredator
ipparam ipredator
lock
noproxyarp
noauth
nobsdcomp
nodeflate
defaultroute
replacedefaultroute
name USERNAMEFORPPTPSERVICE
require-mppe-128
persist
refuse-pap
refuse-eap
refuse-chap
refuse-mschap
noipx
lcp-echo-interval 30
lcp-echo-failure 4

/etc/ppp/chap-secrets
USERNAMEFORPPTPSERVICE ipredator PASSWDFORPPTPSERVICE vpn.ipredator.se

/etc/ppp/ip-up does not contain any customisations.

With that I can start the pptp vpn on the command line as root like that
# while : ; do pon ipredator nodetach debug ; done
using channel 1
Using interface ppp0
Connect: ppp0 <--> /dev/pts/1
sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x3e93cf02> <pcomp> <accomp>]
rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x70400b12> <pcomp> <accomp>]
sent [LCP ConfAck id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x70400b12> <pcomp> <accomp>]
rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x3e93cf02> <pcomp> <accomp>]
sent [LCP EchoReq id=0x0 magic=0x3e93cf02]
rcvd [LCP EchoReq id=0x0 magic=0x70400b12]
sent [LCP EchoRep id=0x0 magic=0x3e93cf02]
rcvd [CHAP Challenge id=0x6e <XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX>, name = "pptpd"]
sent [CHAP Response id=0x6e <YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY>, name = "USERNAMEFORPPTPSERVICE"]
rcvd [LCP EchoRep id=0x0 magic=0x70400b12]
rcvd [CHAP Success id=0x6e "S=ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ"]
CHAP authentication succeeded
sent [CCP ConfReq id=0x1 <mppe +H -M +S -L -D -C>]
rcvd [CCP ConfReq id=0x1 <mppe +H -M +S -L -D -C>]
sent [CCP ConfAck id=0x1 <mppe +H -M +S -L -D -C>]
rcvd [CCP ConfAck id=0x1 <mppe +H -M +S -L -D -C>]
MPPE 128-bit stateless compression enabled
sent [IPCP ConfReq id=0x1 <compress VJ 0f 01> <addr 0.0.0.0>]
rcvd [IPCP ConfReq id=0x1 <compress VJ 0f 01> <addr 93.182.153.2>]
sent [IPCP ConfAck id=0x1 <compress VJ 0f 01> <addr 93.182.153.2>]
rcvd [IPCP ConfNak id=0x1 <addr 93.182.153.41>]
sent [IPCP ConfReq id=0x2 <compress VJ 0f 01> <addr 93.182.153.41>]
rcvd [IPCP ConfAck id=0x2 <compress VJ 0f 01> <addr 93.182.153.41>]
replacing old default route to eth0 [192.168.254.1]
local IP address 93.182.153.41
remote IP address 93.182.153.2
Script /etc/ppp/ip-up started (pid 2867)
Script /etc/ppp/ip-up finished (pid 2867), status = 0x0

So far so good. Now when the computer freezes it looks like that in syslog (please see that attached file)

I noticed that I can (mostly) avoid the freezes if I change the line from the file /etc/ppp/ipredator from:
pty "pptp vpn.ipredator.se --nolaunchpppd"
to
pty "pptp vpn.ipredator.se --nolaunchpppd --timeout 0.3"

I also tried with:
pty "pptp vpn.ipredator.se --nolaunchpppd --timeout 0.5"
but then the freezes still happened, but with timeout 0.3 it seems to work.

However with the setting "timeout 0.3" the overall pptp vpn connection's speed seems to suffer.

I hope that is enough information to debug this problem.

I ran memtest86 for a few hours before investigating this in the first place. RAM seems ok. This computer never freezes unless the pptp connection is running.

A quick search at google yielded these other bug reports:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=424511
http://lists.opensuse.org/opensuse-bugs/2010-08/msg00772.html
http://sourceforge.net/mailarchive/forum.php?thread_name=20100806004326.GK3802%40us.netrek.org&forum_name=pptpclient-devel
http://comments.gmane.org/gmane.comp.misc.pptpclient.devel/2858
http://<email address hidden>/msg22678.html
http://lists.debian.org/debian-devel/2007/05/msg00464.html

BR.
Max.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: pptp-linux 1.7.2-5
ProcVersionSignature: Ubuntu 2.6.35-31.63-generic 2.6.35.13
Uname: Linux 2.6.35-31-generic x86_64
Architecture: amd64
Date: Sat Dec 17 10:33:07 2011
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
ProcEnviron:
 LANGUAGE=de_DE:en
 LANG=de_DE.utf8
 LC_MESSAGES=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: pptp-linux

Revision history for this message
malheum (maxheise) wrote :
Revision history for this message
malheum (maxheise) wrote :

Some additional information.

On another laptop with 32 bits Ubuntu Natty -> Oneiric or 32 bits Linux Mint Katya -> Lisa I could observe the bug with Natty/Katya but not with Oneiric/Lisa anymore.

Revision history for this message
Launchpad Janitor (janitor) wrote :

Status changed to 'Confirmed' because the bug affects multiple users.

Changed in pptp-linux (Ubuntu):
status: New → Confirmed
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