[Bug 966734] Re: nfs4 allows writes by incorrect users

[Toby Corkindale]

/etc/idmapd.conf looks like this at the moment. (I've also tried with
Domain set to another value, or with domain commented out so that imapd
can assign a default automatically, which is the default in the version
of nfs-utils that ships in 12.04)


[General]

Verbosity = 5
Pipefs-Directory = /var/lib/nfs/rpc_pipefs
Domain = localdomain

[Mapping]

Nobody-User = nobody
Nobody-Group = nogroup

[Translation]

Method = nsswitch

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https://bugs.launchpad.net/bugs/966734

Title:
  nfs4 allows writes by incorrect users

Status in “nfs-utils” package in Ubuntu:
  New

Bug description:
  I've observed this bug on Ubuntu Precise (beta) and Oneiric, and also on Debian Squeeze and Debian Testing.
  (Kernel versions 2.6.32, 3.0.0 and 3.2.0)
  I've found numerous forum posts around the internet from confused users, but no solutions.

  The bug in question involves using nfs v4 with the idmapd, with users with the same username but differing uids across the client and server. The idmapping appears to have worked, until you try to write to the directories, at which point it skips the idmapping.
  This is a security issue as it will allow users to access files owned by other users unexpectedly.

  When listing files or directories on the client, the directories show
  up as owned by your local user, however attempting to write will
  result in a Permission Denied error. If you go back to the server and
  chown the directory to be owned by the uid used on the client, then
  the client will see the directory as owned by the incorrect user --
  but WILL be able to write to it!

  The log files for idmapd on both client and server appear to indicate
  that things are working correctly. eg:

  Server's syslog: rpc.idmapd[777]: Server : (user) id "2012" -> name "postie at localdomain"
  Client's syslog: rpc.idmapd[870]: Client 0: (user) name "postie at localdomain" -> id "2014"

  Running commands on the client:
  $ getent passwd postie
  postie:x:2014:2014::/home/postie:/bin/bash
  $ cd /srv/test
  $ ls -l
  drwxr-xr-x 2 postie root 4096 Mar 28 11:48 postie
  $ ls -ln
  drwxr-xr-x 2 2014 0 4096 Mar 28 11:48 postie
  $ touch postie/foo
  touch: cannot touch `postie/foo': Permission denied

  
  To prove that the mount *is* mounted read-write, I'll change the ownership of the directory on the server to uid 2014, rather than the postie user there (who has uid 2012).

  Now I run some commands on the client again:
  $ ls -l
  drwxr-xr-x 2 nobody root 4096 Mar 28 11:48 postie
  $ ls -ln
  drwxr-xr-x 2 65534 0 4096 Mar 28 11:48 postie
  $ touch postie/foo
  # It succeeds!

  
  Any thoughts on this, or if there's a better place to report this bug?

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