lxc-attach crashed with SIGSEGV in get_pty_on_host()

[Philipp]

Installed unity8-lxc, ran unity8-setup, then rebooted.
Login to unity8 lxc session failed (somehow nothing happened), then I logged into Unity7 and the crash happened.

ProblemType: Crash
DistroRelease: Ubuntu 16.04
Package: lxc1 2.0.0~rc15-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-17.33-generic 4.4.6
Uname: Linux 4.4.0-17-generic x86_64
ApportVersion: 2.20.1-0ubuntu1
Architecture: amd64
Date: Wed Apr 6 20:11:34 2016
ExecutablePath: /usr/bin/lxc-attach
InstallationDate: Installed on 2015-12-03 (124 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20151203)
ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-17-generic.efi.signed root=UUID=dccfbc3c-48bc-43ed-9881-36efaa2ef6c5 ro quiet splash vt.handoff=7
SegvAnalysis:
 Segfault happened at: 0x563ee5318994 <main+884>: movl $0x1,0x1c(%r14)
 PC (0x563ee5318994) ok
 source "$0x1" ok
 destination "0x1c(%r14)" (0x0000001c) not located in a known VMA region (needed writable region)!
SegvReason: writing NULL VMA
Signal: 11
SourcePackage: lxc
Stacktrace:
 #0 0x0000563ee5318994 in main ()
 No symbol table info available.
StacktraceTop: main ()
ThreadStacktrace:
 .
 Thread 1 (Thread 0x7fe20540f840 (LWP 2993)):
 #0 0x0000563ee5318994 in main ()
 No symbol table info available.
Title: lxc-attach crashed with SIGSEGV in main()
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:

defaults.conf:
 lxc.network.type = veth
 lxc.network.link = lxcbr0
 lxc.network.flags = up
 lxc.network.hwaddr = 00:16:3e:xx:xx:xx

[Apport retracing service (apport)]

StacktraceTop:
 get_pty_on_host (pid=0x7ffd0fac319c, wrap=0x7ffd0fac31d0, c=0x563ee74ca090) at lxc_attach.c:307
 main (argc=<optimized out>, argv=<optimized out>) at lxc_attach.c:444

[Serge Hallyn (serge-hallyn)]

Thanks for reporting this bug. I haven't reproduced it, but marked it confirmed bc I see how it could happen.

A simple fix would be to not dereference ts without checking for it to be NULL. The question is whether we should be doing more at console_create to not honor lxc.console during attach.

[Serge Hallyn (serge-hallyn)]

Hi,

could you please attach the contents of the file /var/log/lxc/(container).log ?

[Philipp (philipp-pfahofa)]

I did a fresh install of the latest daily build and still I am unable to log into the lxc session in from unity-greeter (same behaviour as before).
But now there is no more popup if I want to report a bug.

If I try 'sudo unity8-lxc-session' this happens:

lxc-attach: attach.c: lxc_attach: 730 failed to get the init pid
/usr/bin/unity8-lxc-session: 30: /usr/bin/unity8-lxc-session: cannot create /proc//root/etc/passwd: Directory nonexistent

[Christian Brauner (cbrauner)]

Hi,

could you please attach the contents of the file /var/log/lxc/(container).log as Serge suggested. That would be great.

[Serge Hallyn (serge-hallyn)]

To be precise, the container name should be unity8-lxc. Please also show it's configuration file, and try

 lxc-ls -f
 lxc-start -n unity-lxc
and if that fails, then
 lxc-start -n unity-lxc -F -l trace -o output

and attach the file 'output'

[Serge Hallyn (serge-hallyn)]

Could you please show the results of:

ls -l /etc/localtime
ls -l /var/lib/lxc/unity8-lxc/rootfs/etc/localtime

?

[Philipp (philipp-pfahofa)]

# ls -l /etc/localtime
-rw-r--r-- 1 root root 2335 Apr 10 23:13 /etc/localtime

# ls -l /var/lib/lxc/unity8-lxc/rootfs/etc/localtime
lrwxrwxrwx 1 root root 27 Apr 10 06:02 /var/lib/lxc/unity8-lxc/rootfs/etc/localtime -> /usr/share/zoneinfo/Etc/UTC

# ls -l /usr/share/zoneinfo/Etc/UTC
lrwxrwxrwx 1 root root 7 Apr 10 23:12 /usr/share/zoneinfo/Etc/UTC -> ../Zulu

# ls -l /usr/share/zoneinfo/Etc/Zulu
lrwxrwxrwx 1 root root 7 Apr 10 23:12 /usr/share/zoneinfo/Etc/Zulu -> ../Zulu

Zulu seems to be a link on itself, that cant work I guess?

[Serge Hallyn (serge-hallyn)]

No that should actually be ok, it's ../Zulu not ./Zulu.

Could you show the contents of

/var/lib/lxc/unity-lxc/config
/var/lib/lxc/unity-lxc/fstab

(I'll also be asking for contents of any files listed in lxc.include lines)

[Philipp (philipp-pfahofa)]

There is no fstab.

I did update my Ubuntu, reinstalled unity8-lxc and created a new lxc container.

Now i get:

# unity8-lxc-session
lxc-attach: attach.c: lxc_attach: 730 failed to get the init pid
/usr/bin/unity8-lxc-session: 30: /usr/bin/unity8-lxc-session: cannot create /proc//root/etc/passwd: Directory nonexistent

# lxc-start -F -n unity8-lxc
lxc-start: utils.c: open_without_symlink: 1623 Too many levels of symbolic links - localtime in /usr/lib/x86_64-linux-gnu/lxc/etc/localtime was a symbolic link!
lxc-start: conf.c: mount_entry: 1650 Too many levels of symbolic links - failed to mount '/etc/localtime' on '/usr/lib/x86_64-linux-gnu/lxc/etc/localtime'
lxc-start: conf.c: lxc_setup: 3730 failed to setup the mount entries for 'unity8-lxc'
lxc-start: start.c: do_start: 819 failed to setup the container
lxc-start: sync.c: __sync_wait: 52 An error occurred in another process (expected sequence number 2)
lxc-start: start.c: __lxc_start: 1329 failed to spawn 'unity8-lxc'
lxc-start: lxc_start.c: main: 344 The container failed to start.
lxc-start: lxc_start.c: main: 348 Additional information can be obtained by setting the --logfile and --logpriority options.

[Serge Hallyn (serge-hallyn)]

Can you confirm that this still happens with ppa:ubuntu-lxc/daily?

[Philipp (philipp-pfahofa)]

Yes.

The ppa updated following packages:

lxc1 amd64 2.0.0+master~20160415-1123-0ubuntu1~xenial
python3-lxc amd64 2.0.0+master~20160415-1123-0ubuntu1~xenial
liblxc1 amd64 2.0.0+master~20160415-1123-0ubuntu1~xenial
lxc-common amd64 2.0.0+master~20160415-1123-0ubuntu1~xenial
lxc-templates amd64 2.0.0+master~20160415-1123-0ubuntu1~xenial

Still I cannot start the session nor update it.

I will upgrade my laptop to Xenial as well soon and try it again with a fresh install on other hardware.

[Philipp (philipp-pfahofa)]

Did a fresh install, could it possibly be that the unity8-lxc package vanished from xenial?
Because I don't know how to create the lxc container by hand.