[Bug 1788459] Re: gssproxy crashes in libselinux.so.1 on Ubuntu 18.04 when called by rpc.gssd

Mon Oct 4 18:32:49 UTC 2021

Performing the verification for Focal.

First, install the problematic package and reproduce the error:

# apt policy gssproxy
gssproxy:
  Installed: 0.8.2-2
  Candidate: 0.8.2-2
  Version table:
 *** 0.8.2-2 500
        500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        100 /var/lib/dpkg/status
# /usr/sbin/gssproxy --interactive --debug --debug-level=3 --socket=/run/gssproxy.sock
[2021/10/04 18:30:15]: Debug Enabled (level: 3)
[2021/10/04 18:30:15]: Keytab /etc/krb5.keytab has no content (-1765328203)
[2021/10/04 18:30:15]: Service: nfs-server, Enckey: [ephemeral], Enctype: 18
[2021/10/04 18:30:15]: Client [2021/10/04 18:30:15]: (/usr/sbin/gssproxy) [2021/10/04 18:30:15]:  connected (fd = 12)[2021/10/04 18:30:15]:  (pid = 1877) (uid = 0) (gid = 0)Segmentation fault (core dumped)

Now, install the version from -proposed and verify that it works correctly:

# apt install gssproxy
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
  gssproxy
1 upgraded, 0 newly installed, 0 to remove and 13 not upgraded.
Need to get 88.4 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu focal-proposed/universe amd64 gssproxy amd64 0.8.2-2ubuntu0.20.04.1 [88.4 kB]
Fetched 88.4 kB in 0s (224 kB/s)    
(Reading database ... 15068 files and directories currently installed.)
Preparing to unpack .../gssproxy_0.8.2-2ubuntu0.20.04.1_amd64.deb ...
Unpacking gssproxy (0.8.2-2ubuntu0.20.04.1) over (0.8.2-2) ...
Setting up gssproxy (0.8.2-2ubuntu0.20.04.1) ...
# apt policy gssproxy
gssproxy:
  Installed: 0.8.2-2ubuntu0.20.04.1
  Candidate: 0.8.2-2ubuntu0.20.04.1
  Version table:
 *** 0.8.2-2ubuntu0.20.04.1 500
        500 http://archive.ubuntu.com/ubuntu focal-proposed/universe amd64 Packages
        100 /var/lib/dpkg/status
     0.8.2-2 500
        500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
# /usr/sbin/gssproxy --interactive --debug --debug-level=3 --socket=/run/gssproxy.sock
[2021/10/04 18:31:59]: Debug Enabled (level: 3)
[2021/10/04 18:31:59]: Keytab /etc/krb5.keytab has no content (-1765328203)
[2021/10/04 18:31:59]: Service: nfs-server, Enckey: [ephemeral], Enctype: 18
[2021/10/04 18:31:59]: Client [2021/10/04 18:31:59]: (/usr/sbin/gssproxy) [2021/10/04 18:31:59]:  connected (fd = 12)[2021/10/04 18:31:59]:  (pid = 2244) (uid = 0) (gid = 0)[2021/10/04 18:31:59]: 
^C[2021/10/04 18:32:10]: Exiting after receiving a signal

Therefore, the new package indeed fixes the problem.

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https://bugs.launchpad.net/bugs/1788459

Title:
  gssproxy  crashes in libselinux.so.1 on Ubuntu 18.04 when called by
  rpc.gssd

Status in gssproxy package in Ubuntu:
  In Progress
Status in libselinux package in Ubuntu:
  Invalid
Status in gssproxy source package in Focal:
  Fix Committed
Status in libselinux source package in Focal:
  Invalid
Status in gssproxy source package in Hirsute:
  Fix Committed
Status in libselinux source package in Hirsute:
  Invalid

Bug description:
  [ Impact ]

  gssproxy users on Focal and Hiruste who configure the package to
  handle NFS mountpoints using Kerberos authentication will experience a
  segmentation fault when invoking the service either through systemd or
  by hand.

  [ Test Case]

  Inside a Focal LXD container:

  $ lxc launch images:ubuntu/focal gssproxy-bug1788459-focal
  $ lxc shell gssproxy-bug1788459-focal
  # apt update
  # apt install -y gssproxy nfs-kernel-server
  # cat > /etc/gssproxy/gssproxy.conf << __EOF__
  [gssproxy]
  debug = true
  debug_level = 3
  __EOF__
  # cat >> /etc/gssproxy/25-nfs-server.conf << __EOF__
  [service/nfs-server]
  mechs = krb5
  socket = /run/gssproxy.sock
  cred_store = keytab:/etc/krb5.keytab
  trusted = yes
  kernel_nfsd = yes
  euid = 0
  __EOF__
  # /usr/sbin/gssproxy --interactive --debug --debug-level=3 --socket=/run/gssproxy.sock
  [2021/06/30 14:34:14]: Debug Enabled (level: 3) 
  [2021/06/30 14:34:14]: Keytab /etc/krb5.keytab has no content (-1765328203)
  [2021/06/30 14:34:14]: Service: nfs-server, Enckey: [ephemeral], Enctype: 18
  [2021/06/30 14:34:14]: Client [2021/06/30 14:34:14]: (/usr/sbin/gssproxy) [2021/06/30 14:34:14]:  connected (fd = 12)[2021/06/30 14:34:14]:  (pid = 3428) (uid = 0) (gid = 0)Segmentation fau
  lt (core dumped)

  [ Where problems could occur ]

  * The backported patch is simple and it is very unlikely that it will introduce a regression.
  * As usual, it is always risky to rebuild a package that hasn't been touched for more than 1 year, albeit in this case the risk is very low because the package is not very complex.

  [ Original Description ]

  I have apache configured to perform a kerberized NFS4 mount using
  rpc.gssd and gssproxy.

  If I request a web page that requires NFS4 access, then gssproxy
  crashes, reporting a segfault in libselinux.so.1 and the web request
  generates a 403 error.

  gssproxy[6267]: segfault at 0 ip 00007f2f5bb1951a sp 00007ffe861da150
  error 4 in libselinux.so.1[7f2f5bb0d000+25000]

  If I run gssproxy at debug level = 3, and then load a web page, I can
  see the uid/principal request for www-data come in from rpc.gssd:

  # gssproxy -d --debug-level=3 -i -C /etc/gssproxy

  [2018/08/22 17:51:40]: Debug Enabled (level: 3)
  [2018/08/22 17:52:06]: Client [2018/08/22 17:52:06]: (/usr/sbin/rpc.gssd) [2018/08/22 17:52:06]:  connected (fd = 10)[2018/08/22 17:52:06]:  (pid = 4548) (uid = 33) (gid = 33)Segmentation fault (core dumped)

  Since gssproxy is required to initiate kerberos principals for any
  local application services - Ubuntu 18.04 does not currently support
  running application services with NFS4 kerberos dependencies.  This
  has a fairly significant impact on anyone attempting to implement
  kerberos on Ubuntu 18.04

  Ubuntu 18.04.1 LTS
  gssproxy 0.8.0-1
  libselinux1:amd64 2.7-2build2
  libgssrpc4:amd64 1.16-2build1

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