Ubuntu
util-linux package

'unmount' fails for user mounted file system

Bug #295944 reported by Ken Pratt
30
This bug affects 4 people
Affects Status Importance Assigned to Milestone
util-linux (Ubuntu)
Confirmed
Undecided
Unassigned

Bug Description

Binary package hint: mount

I use an encrypted ext3 file system stored in a file. I mount this file system through the cryptoloop module and a loop device. This approach worked fine in 8.04. On a fresh install of 8.10 amd64 Desktop, I receive the following when I attempt to unmount the user mounted filesystem.

umount: /mnt/secure mount disagrees with the fstab

Here is the line in my fstab file:

/media/BigData/secure.img /mnt/secure auto user,noauto,loop,encryption=twofish 0 0

As a regular user, I am able to execute 'mount /mnt/secure'. I get prompted for a password and the file system is mounted on /mnt/secure as usual.

When I attempt 'umount /mnt/secure', I get the error cited above. If I become root, then I am able to unmount the file system. I should be able to do it as the user that originally mounted the file system.

* I marked the bug as a security vulnerability as it requires 'root' privileges to unmount a user mounted file system.

Revision history for this message
Henning Mersch (ubuntu-hmersch) wrote :

Same here (Kubuntu 8.10, 32bit Desktop, backports enabled...)

No attention to this? Very strange .... nobody encrypting their USB Sticks, which
would (I think) use this princip?

As a workaround I added
/dev/loop0 /mnt/secure auto user,noauto,loop,encryption=twofish 0 0
to the fstab, which enabled user to unmount ... BUT:
... this means I have TO PRAY that /mnt/secure is mounted via loop0 ...

Regards - Henning

Kees Cook (kees)
Changed in util-linux (Ubuntu):
status: New → Confirmed
Revision history for this message
Kevin Smith (ubuntu-qualitycode) wrote :

This is not just for encrypted mounts. I have an hfsplus loopback mount and cannot umount it. This worked fine in 8.04, but fails in 9.04.

Here is my /etc/fstab:

  /home/j2ee-hudson/Miradi/Miradi.dmg /mounts/Miradi/dmgfile hfsplus rw,user,loop,noauto 0 0

Here is my mount command:

  mount -v /mounts/Miradi/dmgfile

Here is what ends up in /etc/mtab:

  /dev/loop0 /mounts/Miradi/dmgfile hfsplus rw,noexec,nosuid,nodev,user=kevins 0 0

And here is my attempt to unmount as non-root:

  > umount -d /mounts/Miradi/dmgfile
  umount: /mounts/Miradi/dmgfile mount disagrees with the fstab

I'm a software developer, and my automated builds are now failing because of this. The workaround mentioned above (adding a /dev/loop0 line to fstab) does work, but also makes me quite nervous.

Revision history for this message
infodroid (infodroid) wrote :

@Kevin. This is an ugly hack. But if you put your second line beginning with "/dev/loop0" into your /etc/fstab, then you will be able to run the unmount for your /mounts dmgfile. Just remember to add noauto so it doesn't mount twice on bootup.

Revision history for this message
Daniel Harvey (daniel.harvey) wrote :

The hack works. Quick note that you can specify the loop device in both lines, which is a little safer than assuming loop0 i.e.

/media/USBDISK/.fs.ext3 /media/USBDISK/fs ext2 defaults,noauto,loop=/dev/loop3,user,exec 0 0
/dev/loop3 /media/USBDISK/fs ext2 defaults,noauto,loop=/dev/loop3,user,exec 0 0

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