Crashes with "short read" with default ppp0 MTU

[Nicolás Lichtmaier]

Binary package hint: pptp-linux

When I log in to my work VPN from a place in which I have an ethernet connection (instead of WiFi), the VPN drops with these messages in syslog:

Jun 2 18:54:11 axolotl pptp[301]: nm-pptp-service-32762 log[decaps_gre:pptp_gre.c:414]: buffering packet 22 (expecting 21, lost or reordered)
Jun 2 18:54:14 axolotl pptp[301]: nm-pptp-service-32762 warn[decaps_gre:pptp_gre.c:331]: short read (-1): Message too long
Jun 2 18:54:14 axolotl pptp[308]: nm-pptp-service-32762 log[callmgr_main:pptp_callmgr.c:234]: Closing connection (unhandled)
Jun 2 18:54:14 axolotl pptp[308]: nm-pptp-service-32762 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 12 'Call-Clear-Request'
Jun 2 18:54:14 axolotl pptp[308]: nm-pptp-service-32762 log[call_callback:pptp_callmgr.c:79]: Closing connection (call state)
Jun 2 18:54:14 axolotl pppd[32764]: Modem hangup
Jun 2 18:54:14 axolotl pppd[32764]: Connect time 0.5 minutes.
Jun 2 18:54:14 axolotl pppd[32764]: Sent 1319 bytes, received 1158 bytes.
Jun 2 18:54:14 axolotl pppd[32764]: MPPE disabled
Jun 2 18:54:14 axolotl pppd[32764]: Connection terminated.

If I set up ppp0 MTU to 500 it doesn't crash (it does with 1200!). I don't know in which package the bug is exactly (I set up the VPN from network manager). If this is not the right package to report this, please reassign it, thanks!

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: pptp-linux 1.7.2-4
ProcVersionSignature: Ubuntu 2.6.32-22.33-generic 2.6.32.11+drm33.2
Uname: Linux 2.6.32-22-generic x86_64
NonfreeKernelModules: nvidia
Architecture: amd64
Date: Wed Jun 2 19:00:56 2010
ProcEnviron:
 LANGUAGE=es_AR:es
 PATH=(custom, user)
 LANG=es_AR.UTF-8
 SHELL=/bin/bash
SourcePackage: pptp-linux

[Nicolás Lichtmaier (niqueco)]

This has to do with MTU path discovery. The weird thing (to me) is that EMSGSIZE is being sent by the kernel in the "read" call instead of when the data is being sent. The client does not expect that and ends.

[Jeff Breadner (jbreadner)]

The following is a little heavy handed, but it works:

echo 1 >/proc/sys/net/ipv4/ip_no_pmtu_disc

[Launchpad Janitor (janitor)]

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

[Cilidariu Mihai-Daniel (cmlist)]

This also works:

ifconfig eth0 mtu 1200