Mounting a loop device causes the wrong loop device to be mounted.

[Jon Brase]

Ubuntu 10.04.3 LTS
util-linux 2.17.2-0ubuntu1.10.04.2

There may be other packages involved in this bug than util-linux: This bug has only affected me for a few days, whereas Synaptic reports the last update to util-linux / mount to have been about a year ago (January 20th 2011).

After setting up a loop device with losetup, mounting that loop device will cause the next available loop device to be mounted instead of the designated loop device. If the loop devices are listed in fstab, this will trigger bug 726283 when an unprivileged user attempts to unmount them.

For example, with an fstab containing the following lines:

/dev/loop0 /mnt/loop0 auto loop,user,noauto 0 0
/dev/loop1 /mnt/loop1 auto loop,user,noauto 0 0
/dev/loop2 /mnt/loop2 auto loop,user,noauto 0 0
/dev/loop3 /mnt/loop3 auto loop,user,noauto 0 0
/dev/loop4 /mnt/loop4 auto loop,user,noauto 0 0
/dev/loop5 /mnt/loop5 auto loop,user,noauto 0 0

And the following commands given:

losetup /dev/loop0 image0.img
losetup /dev/loop1 image1.img
mount /dev/loop0
mount /dev/loop1

The following lines will be produced in /etc/mtab:

/dev/loop2 /mnt/loop0 iso9660 rw,noexec,nosuid,nodev,user=username 0 0
/dev/loop3 /mnt/loop1 iso9660 rw,noexec,nosuid,nodev,user=username 0 0

And losetup -f will produce the following:

/dev/loop4

Attempting to umount /dev/loop0 or /dev/loop1 will produce:

umount: /dev/loop[loop device number we attempted to umount] is not mounted (according to mtab)

And attempting to umount /dev/loop2 or /dev/loop3 as an unprivileged user will trigger bug 726283, as /etc/fstab and /etc/mtab are inconsistent with each other as to which loop devices are associated with which directories.

In short:
Expected result: The commands given above should result in the following mtab lines and losetup -f output:

mtab:
/dev/loop0 /mnt/loop0 iso9660 rw,noexec,nosuid,nodev,user=username 0 0
/dev/loop1 /mnt/loop1 iso9660 rw,noexec,nosuid,nodev,user=username 0 0

losetup -f:
/dev/loop2

Actual result: The commands given above result in the following mtab lines and losetup -f output:

mtab:
/dev/loop2 /mnt/loop0 iso9660 rw,noexec,nosuid,nodev,user=username 0 0
/dev/loop3 /mnt/loop1 iso9660 rw,noexec,nosuid,nodev,user=username 0 0

losetup -f:
/dev/loop4

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: mount 2.17.2-0ubuntu1.10.04.2
ProcVersionSignature: Ubuntu 2.6.32-38.83-generic 2.6.32.52+drm33.21
Uname: Linux 2.6.32-38-generic x86_64
NonfreeKernelModules: nvidia
Architecture: amd64
Date: Sat Jan 21 10:40:28 2012
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/zsh
SourcePackage: util-linux

[Jon Brase (jonathan-brase)]

Oops. Just realized that the problem was do to the inclusion of "loop,user,noauto" rather than "user,noauto" in my fstab entries.

[Ayan George (ayan)]

So it is safe to say this is invalid? I'm marking it as such. Please update the bug if the case is otherwise.