[plug] loopback

[Cameron Patrick]

Jim Householder wrote:

> $ mount file.iso /distros/loop0-t iso9660 -o loop=/dev/loop0
> which works nicely under Mdk 10, but gives me
> ioctl: LOOP_SET_FD: Device or resource busy.

Looking at the kernel source, the most likely cause for that error is
that /dev/loop0 is already in use.  That's okay, though, because there
are (by default) 8 loop devices, which is enough for most people.  (It
can be increased further with the max_loop option to the loop module,
for those occasions where you feel like doing freaky things with loop
mounts.)  Normally you just specify '-o loop' without naming a device
and it'll find the first free loop device.

> Also, the command is rejected if not issued by root.

That's normal.  Only root can mount or unmount things (with a few
exceptions, e.g. devices listed with the 'user' option in /etc/fstab).

Loop-mounting an arbitrary filesystem - even onto a mount point that
you own - can be a security hole.  Consider the case of creating an
ext2 filesystem image with a setuid copy of bash on it, copying it to
someone else's machine and loop-mounting it somewhere.

Cameron.