sudoedit triggers pam_mount to enquire the password of the encrypted partition, trying to mount it and later to umount it.

Bug #996806 reported by Jari Laamanen on 2012-05-08
56
This bug affects 10 people
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user-mounts
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sudo (Ubuntu)
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Bug Description

I have sudo 1.8.3p1-1ubuntu3.1 from precise-proposed and I use pam_mount for mounting encrypted partitions at login. (LVM partitions, if that matters.)

'sudoedit' command triggers pam_mount to enquire the password of the encrypted partition, trying to mount it and later to umount it. Mounting and umounting fails, because the encrypted partition is already mounted, unlocked and busy. The edited file is not changed rendering sudoedit useless.

$ sudoedit test
reenter password for pam_mount:
pam_mount(mount.c:69): Messages from underlying mount program:
pam_mount(mount.c:73): crypt_activate_by_passphrase: File exists
pam_mount(pam_mount.c:521): mount of /dev/myvolumehere/mypartitionhere failed
pam_mount(mount.c:69): umount messages:
pam_mount(mount.c:73): umount: /mnt/mymountedpartition: device is busy.
pam_mount(mount.c:73): (In some cases useful info about processes that use
pam_mount(mount.c:73): the device is found by lsof(8) or fuser(1))
pam_mount(mount.c:73): umount /mnt/mymountedpartition failed with run_sync status 1
pam_mount(mount.c:73): umount: /mnt/mymountedpartition: device is busy.
pam_mount(mount.c:73): (In some cases useful info about processes that use
pam_mount(mount.c:73): the device is found by lsof(8) or fuser(1))
pam_mount(mount.c:73): umount /mnt/mymountedpartition failed with run_sync status 1
pam_mount(mount.c:752): unmount of /dev/myvolumehere/mypartitionhere failed

If I edit the file "test", the tmp file "/var/tmp/test.XXN2W9z4" gets updated, but after exiting sudoedit, the actual file is not changed. The tmp file is removed after exiting.

sudo (version 1.8.3p1-1ubuntu3.1) does not trigger this behavior, just sudoedit. If I clear the sudo timestamp:
$ sudo -k
$ sudoedit test
[sudo] password for myusername:
pam_mount(mount.c:69): Messages from underlying mount program:
[...the same errors...]

If I donwgrade to version sudo=1.8.3p1-1ubuntu3, the sudoedit fails similarly, but appended with the known bug 927828:

shell:~$ sudoedit test
reenter password for pam_mount:
pam_mount(mount.c:69): Messages from underlying mount program:
pam_mount(mount.c:73): crypt_activate_by_passphrase: File exists
pam_mount(pam_mount.c:521): mount of /dev/myvolumehere/mypartitionhere failed
sudoedit: pam_mount.c:417: modify_pm_count: Assertion `user != ((void *)0)' failed.
Aborted
shell:~$ ls test
ls: cannot access test: No such file or directory

So sudoedit was unusable also with the old version.

The workaround is to edit files using "sudo vim (file)"

$ lsb_release -rd
Description: Ubuntu 12.04 LTS
Release: 12.04

sudo:
  Installed: 1.8.3p1-1ubuntu3.1

/$ cat /etc/pam.d/sudo
#%PAM-1.0
@include common-auth
@include common-account
@include common-session-noninteractive

$ grep pam_mount /etc/pam.d/common-*
/etc/pam.d/common-auth:auth optional pam_mount.so
/etc/pam.d/common-session:session optional pam_mount.so
/etc/pam.d/common-session-noninteractive:session optional pam_mount.so

Hence, pam_mount.so is in both common-auth and common-session-noninteractive. However, sudo does not have this problem, only sudoedit.

File /etc/security/pam_mount.conf.xml:

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE pam_mount SYSTEM "pam_mount.conf.xml.dtd">
<pam_mount>
<debug enable="0" />
<mntoptions allow="nosuid,nodev,loop,encryption,fsck,nonempty,allow_root,allow_other" />
<mntoptions require="nosuid,nodev" />
<logout wait="0" hup="0" term="0" kill="0" />
<mkmountpoint enable="1" remove="true" />
<volume user="myusername" fstype="crypt" path="/dev/myvolumehere/mypartitionhere" mountpoint="/mnt/mymountedpartition" />
</pam_mount>

TJ (tj) on 2012-05-09
Changed in sudo (Ubuntu):
assignee: nobody → TJ (intuitivenipple)
status: New → In Progress
aldebx (aldebx) wrote :

As reported by Stewart Prescott [1], this error is triggered when the system invokes pam-mount twice, which means that pam-mount tries to mount the volume twice as a result and the second time fails because the mount point is not empty.

Currently, this seems to be a bug of the default packaging rather than an user misconfiguration since even by resetting to default values via command

 pam-auth-update

do not fix the situation. In Ubuntu 12.04 pam-mount is referenced in 3 files:

common-auth
common-session
common-session-noninteractive

and given that /etc/pam.d/sudo calls
#%PAM-1.0
@include common-auth
@include common-account
@include common-session-noninteractive

therefore pam-mount is called twice (common-auth and common-noninteractive)

By removing (commenting out) the reference to pam-mount in "common-session-noninteractive" this error does not appear any more, without compromising any feature on non-server machines.

By the way, in my case the exact same error referenced in this bug does not appear only with sudoedit, but also with sudo itself updated to the latest version 1.8.3p1-1ubuntu3.1

[1] http://nanonanonano.net/linux/debian/enchome

Moritz Hassert (mhassert) wrote :
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Hi, I'm affected too and would like to provide some additional information:

I suspect this bug is not caused by _how often_ pam_mount is called but rather a mixup of the user it is run under.
When running sudoedit, before the editor component is started, pam_mount always tries to mount the partition. So while the editor is shown, the partition is always mounted. Either because it has been mounted before or because it got mounted here.
pam_mount also increases the login-count of the normal user (not root!) issuing the sudoedit command.
After you close the editor pam_mount decreases the login count for root (not the above user!) and as there are no counted logins for root, it always decides to unmount the partition. So after sudoedit is finished the partition is always unmounted regardless of its state before running sudoedit. So after using sudoedit for the first time after kdm/whatever login the mount is gone.

It seems to me, sudoedit is opening a new session for user $USER but then closing one for user "root".

See the following log produced with pam_mount debugging enabled:
[BEGIN OF LOG]
USER@USER:~$ cat /var/run/pam_mount/USER
0x3

USER@USER:~$ LC_ALL=C sudoedit foo
[sudo] password for USER:
pam_mount(pam_mount.c:364): pam_mount 2.10: entering auth stage
pam_mount(pam_mount.c:553): pam_mount 2.10: entering session stage
pam_mount(misc.c:38): Session open: (ruid/rgid=0/2000, e=0/2000)
pam_mount(mount.c:218): Mount info: globalconf, user=USER <volume fstype="crypt" server="(null)" path="/dev/disk/by-uuid/UUID_OF_LUKS_PARTITION" mountpoint="/media/data" cipher="(null)" fskeypath="(null)" fskeycipher="(null)" fskeyhash="(null)" options="fsck,acl,user_xattr,relatime" /> fstab=0 ssh=0
command: 'mount' '-t' 'crypt' '-ofsck,acl,user_xattr,relatime' '/dev/disk/by-uuid/UUID_OF_LUKS_PARTITION' '/media/data'
pam_mount(misc.c:38): set_myuid<pre>: (ruid/rgid=0/2000, e=0/2000)
pam_mount(misc.c:38): set_myuid<post>: (ruid/rgid=0/2000, e=0/2000)
  [... pam_mount(misc.c:380): ... [List of all previously active mounts ...]
  [the newly mounted partition:]
pam_mount(misc.c:380): 21 20 252:5 / /media/data rw,relatime - ext4 /dev/mapper/_dev_dm_2 rw,user_xattr,acl,barrier=1,data=ordered
command: 'pmvarrun' '-u' 'USER' '-o' '1'
pam_mount(misc.c:38): set_myuid<pre>: (ruid/rgid=0/2000, e=0/2000)
pam_mount(misc.c:38): set_myuid<post>: (ruid/rgid=0/2000, e=0/2000)
pmvarrun(pmvarrun.c:252): parsed count value 3
pam_mount(pam_mount.c:440): pmvarrun says login count is 4
pam_mount(pam_mount.c:645): done opening session (ret=0)
Processing '/etc/joe/editorrc'...Processing '/etc/joe/ftyperc'...done
done

  [... editor opens. close it without saving ...]

File /var/tmp/foo.XXOuqivj not changed so no update needed
pam_mount(pam_mount.c:691): received order to close things
pam_mount(misc.c:38): Session close: (ruid/rgid=0/2000, e=0/2000)
command: 'pmvarrun' '-u' 'root' '-o' '-1'
pam_mount(misc.c:38): set_myuid<pre>: (ruid/rgid=0/2000, e=0/2000)
pam_mount(misc.c:38): set_myuid<post>: (ruid/rgid=0/2000, e=0/2000)
pmvarrun(pmvarrun.c:252): parsed count value 0
pam_mount(pam_mount.c:438): error reading login count from pmvarrun
pam_mount(mount.c:749): going to unmount
pa...

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Moritz Hassert (mhassert) wrote :
Download full text (3.4 KiB)

Just checked sudo's behavior regarding the login count. It consistently uses the user "root" before and after the given command:

[BEGIN OF LOG]
[sudo] password for USER:
pam_mount(pam_mount.c:364): pam_mount 2.10: entering auth stage
pam_mount(pam_mount.c:553): pam_mount 2.10: entering session stage
pam_mount(misc.c:38): Session open: (ruid/rgid=1014/2000, e=0/2000)
pam_mount(pam_mount.c:614): no volumes to mount
command: 'pmvarrun' '-u' 'root' '-o' '1'
pam_mount(misc.c:38): set_myuid<pre>: (ruid/rgid=1014/2000, e=0/2000)
pam_mount(misc.c:38): set_myuid<post>: (ruid/rgid=0/2000, e=0/2000)
pmvarrun(pmvarrun.c:252): parsed count value 0
pam_mount(pam_mount.c:440): pmvarrun says login count is 1
pam_mount(pam_mount.c:645): done opening session (ret=0)
uid=0(root) gid=0(root) Gruppen=0(root)
pam_mount(pam_mount.c:691): received order to close things
pam_mount(pam_mount.c:693): No volumes to umount
command: 'pmvarrun' '-u' 'root' '-o' '-1'
pam_mount(misc.c:38): set_myuid<pre>: (ruid/rgid=1014/2000, e=0/2000)
pam_mount(misc.c:38): set_myuid<post>: (ruid/rgid=0/2000, e=0/2000)
pmvarrun(pmvarrun.c:252): parsed count value 1
pam_mount(pam_mount.c:440): pmvarrun says login count is 0
pam_mount(pam_mount.c:728): pam_mount execution complete
pam_mount(pam_mount.c:115): Clean global config (1073741824)
pam_mount(pam_mount.c:132): clean system authtok=0x151b270 (1073741824)
[END OF LOG]

@aldebx:
I can reproduce your problem with sudo in version 1.8.3p1-1ubuntu3.2:
My mount-line in /etc/security/pam_mount.conf.xml is limited to user "user=USER". If I change this to "user=root" or remove the limitation altogether, I get "reenter password for pam_mount" when running "sudo id". Can you confirm this is similar to your config?

Without such a change to my configs, you can see in the above sudo log that pam_mount would like to mess with mounts too but can't because there are none available for user root ("no volumes to mount").

So IMHO there are two different issues to address:

1. fixing sudo/sudoedit:
sudoedit's interaction with pam_mount regarding the user is bogus. It should be just like sudo does it. (Why is it different in the first place?)

2. fixing pam_mount:
- First, there are good reasons to run pam_mount from sudo: Consider a user cron job running "sudo foo" where the user is allowed (by /etc/sudoers) to run "sudo foo" without entering a password. The Command "foo" may need access to a certain partition. The partition may be mounted on-demand by pam_mount for various reasons (to save resources, ...).
- But there is absolutely no use in asking for a unlock password in this use case. So pam_mount should skip encrypted partitions if there is no way to ask for a password (This may already be the current behavior. I haven't tested it.)
- If there is an encrypted partition for user root available that is not yet mounted and we're in an interactive shell, ask for the password to unlock it. If root does not need the mount, then don't configure it this way.
- If a partition is already mounted by pam_mount, even because of another users login-session, pam_mount should not try to mount it again and therefore not ask for a password. It should keep track o...

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Jari Laamanen (yartsa) wrote :

Thanks Moritz for debugging, I believe that you are correct. Especially as my /etc/security/pam_mount.conf.xml contains instructions only for the user, not root, I did not get any trouble with sudo.

aldebx (aldebx) wrote :

I am orphaning the bug given that there has been no interaction with the assignee since the bug has been opened. If you are still interested in fixing this bug, please drop a line on the work progress. Thanks.

Changed in sudo (Ubuntu):
assignee: TJ (intuitivenipple) → nobody
status: In Progress → Confirmed
aldebx (aldebx) wrote :

@ Moritz - Thank you for your insightful debugging of this issue. As you anticipated, I confirm that restricting the directive in pam_mount.xml to a specific user (user="USERNAME") is a valid workaround.

I also would like to add that my suggested workaround (i.e. commenting out @pam-mount in "common-session-noninteractive" breaks authentication systems used also on desktop systems. Please discard it.

Jari Laamanen (yartsa) wrote :

aldebx, by "restricting the directive in pam_mount.xml to a specific user " workaround you mean sudo, as for sudoedit there is no workaround? Or does sudoedit behave normally for you after editing just pam_mount.xml?

Moritz Hassert (mhassert) wrote :

Haven't seen this problem for a while and just tested on 14.04: Seems it has been fixed somewhere in the last two years.

So I guess this bug report could be closed.

Marcus Sentry (thesentry) wrote :

@Jari: Just tested it myself, I added (user="USERNAME") to my pam_mount.xml and it works now.

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