Ubuntu – Creating disk images as a normal user

I want to be able to run the following script as normal user (as root it runs fine):

#!/bin/sh

dd if=/dev/zero bs=8192 count=128 of=disk.img
mkfs -t ext2 -F disk.img
losetup /dev/loop0 disk.img
mount /dev/loop0
echo aaaa > /mnt/aa
umount /mnt
losetup -d /dev/loop0

To that end, I

1) added appropriate entry to /etc/fstab (only then normal user can run 'mount /dev/loop0' ):

/dev/loop0  /mnt  ext2    defaults,loop,users,noauto      0 0

2) added the user in question to the 'disk' group (only then the user is able to run 'losetup' – /dev/loop0 is owned by the 'disk' group)

Now, hopefully the last problem is that when I run as normal user, I get 'permission denied' error from 'echo'. No wonder, because after mounting, the permissions of the /mnt directory change to 755 root:root, and obviously a normal user cannot create files inside.

How should I create my 'disk.img' so that when mounted it is writeable by the very user that created it?

Edit:

The proposed 'pmount' solution appears to have the same problem. Reproduction steps:

1) install 'pmount' and add '/dev/loop0' to /etc/pmount.allow

2) run the following as a normal user:

#!/bin/sh

dd if=/dev/zero bs=8192 count=128 of=disk.img
mkfs -t ext2 -F disk.img
losetup /dev/loop0 disk.img
pmount -w /dev/loop0
echo aaaa > /media/loop0/aa
pumount /media/loop0
losetup -d /dev/loop0

You will still get 'permission denied' from echo for the same reason we got it before – the permissions of the /media/loop0/ directory are 755:

[user@server test]$ ls -l /media/
total 1
drwxr-xr-x 3 root root 1024 Jul 22 13:40 loop0
[user@server test]$ ls -l /media/loop0/
total 12
drwx------ 2 root root 12288 Jul 22 13:40 lost+found

Edit2:

I managed to solve this – option 'root_owner' to mkfs.ext3 comes in handy:

#!/bin/sh

WHOAMI=`whoami`

uid=$(id -u $WHOAMI)
gid=$(id -g $WHOAMI)

dd if=/dev/zero bs=8192 count=128 of=disk.img
mkfs.ext3 -E root_owner=$uid:$gid disk.img
losetup /dev/loop0 disk.img
mount /dev/loop0
echo aaaa > /mnt/aa
umount /mnt
losetup -d /dev/loop0

Then after mounting the mountpoint is owned by the user who is running the script, and then the user is able to write inside 🙂