sshd: preauth child terminated by signal 11

[IC Raibow]

Can't connect to a local installation of openssh-server.

ssh localhost fails with "Broken pipe", here's the tail of ssh -vv:

...
debug1: Enabling compression at level 6.
debug1: Authentication succeeded (publickey).
Authenticated to localhost ([127.0.0.1]:22).
debug1: channel 0: new [client-session]
debug2: channel 0: send open
debug1: Requesting <email address hidden>
debug1: Entering interactive session.
Write failed: Broken pipe

Those lines are appearing in auth.log:

Sep 26 14:09:10 natali sshd[6076]: Accepted publickey for wiz from 127.0.0.1 port 48624 ssh2
Sep 26 14:09:10 natali sshd[6076]: fatal: privsep_preauth: preauth child terminated by signal 11

Also, any ssh invocation (even -h) ends with "Segmentation fault":

usage: ssh [-1246AaCfgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec]
           [-D [bind_address:]port] [-e escape_char] [-F configfile]
           [-I pkcs11] [-i identity_file]
           [-L [bind_address:]port:host:hostport]
           [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]
           [-R [bind_address:]port:host:hostport] [-S ctl_path]
           [-W host:port] [-w local_tun[:remote_tun]]
           [user@]hostname [command]
Segmentation fault

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: openssh-server 1:6.0p1-3ubuntu1
ProcVersionSignature: Ubuntu 3.5.0-15.22-generic 3.5.4
Uname: Linux 3.5.0-15-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.5.2-0ubuntu4
Architecture: amd64
Date: Wed Sep 26 14:01:24 2012
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Alpha amd64 (20120724.2)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SSHDConfig: Error: command ['pkexec', '/usr/sbin/sshd', '-T'] failed with exit code -11:
SourcePackage: openssh
UpgradeStatus: No upgrade log present (probably fresh install)

[Serge Hallyn (serge-hallyn)]

Can you please post /etc/ssh/sshd_config, /etc/pamd./sshd on the server? Is there anything in /var/log/syslog or /var/log/kern.log?

If you have admin rights on the server, you could determine the exact location of the segfault by installing the openssh-server-dbgsym package as described in https://wiki.ubuntu.com/DebuggingProgramCrash.

[IC Raibow (icrbow)]

/var/log/kern.log is littered with libkrb5support.so errors:

kernel: [ 7.097781] do_general_protection: 60 callbacks suppressed
kernel: [ 7.097786] colord-sane[1046] general protection ip:7f36ab9ccfe0 sp:7fff3368c538 error:0 in libkrb5support.so.0.1[7f36ab9cb000+7000]
kernel: [ 7.541893] host[1803] general protection ip:7f29dce5cfe0 sp:7fff60978ea8 error:0 in libkrb5support.so.0.1[7f29dce5b000+7000]
kernel: [ 7.562644] host[1842] general protection ip:7f9be27ddfe0 sp:7fff23e7e398 error:0 in libkrb5support.so.0.1[7f9be27dc000+7000]
kernel: [ 23.745531] ssh[2523] general protection ip:7f3672bb7fe0 sp:7fff9bd41228 error:0 in libkrb5support.so.0.1[7f3672bb6000+7000]
kernel: [ 28.182345] ssh[2535] general protection ip:7fb9b184bfe0 sp:7fffec75a918 error:0 in libkrb5support.so.0.1[7fb9b184a000+7000]
kernel: [ 30.195913] ssh[2559] general protection ip:7f6d3653efe0 sp:7fff9f30e1c8 error:0 in libkrb5support.so.0.1[7f6d3653d000+7000]

There's also an error when i run ssh under gdb:

(gdb) run
Starting program: /usr/bin/ssh
Error while mapping shared library sections:
`/usr/lib/x86_64-linux-gnu/libkrb5support.so.0': not in executable format: File format not recognized

[IC Raibow (icrbow)]

Looks like reinstalling the same version of libkrb5support resolved the issue.