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General Information
===================
FUSE (Filesystem in USErspace) is a simple interface for userspace
programs to export a virtual filesystem to the linux kernel. FUSE
also aims to provide a secure method for non privileged users to
create and mount their own filesystem implementations.
You can download the source code releases from
http://sourceforge.net/projects/avf
or alternatively you can use CVS to get the very latest development
version: set the cvsroot to
:pserver:anonymous@cvs.avf.sourceforge.net:/cvsroot/avf
and check out the 'fuse' module.
Installation
============
See the file 'INSTALL'
IMPORTANT NOTE: If you run a system with untrusted users, installing
this program is not recommended, as it could be used to breach
security (see the 'Security' section for explanation).
How To Use
==========
FUSE is made up of three main parts:
- A kernel filesystem module (kernel/fuse.o)
- A userspace library (lib/libfuse.a)
- A mount/unmount program (util/fusermount)
Here's how to create your very own virtual filesystem in five easy
steps:
1) Edit the file example/fusexmp.c to do whatever you want...
2) Build the fusexmp program
3) run 'util/fusermount /mnt/whatever example/fusexmp -d'
4) ls -al /mnt/whatever
5) Be glad!
If it doesn't work out, you can ask the me. (Oh yeah, and you need to
do 'insmod kernel/fuse.o' before running your program, in case you
forgot).
See the file 'include/fuse.h' for documentation of the library interface.
Security
========
If you run 'make install', the fusermount program is installed
set-user-id to root. This is done to allow normal users to mount
their own filesystem implementations.
There must however be some limitations to forbid the Bad User to do
Naughty Things with your Beautiful system. Currently those
limitations are:
- The user can only mount on a mountpoint, for which it has write
permission
- The mountpoint is not a sticky directory which isn't owned by the
user (like /tmp usually is)
- If the user doing the mount is not root, then no other user
(including root) can access the contents of the mounted
filesystem.
When linux will have private namespaces (as soon as version 2.5 comes
out) then this third condition is useless and can be gotten rid of.
Currently the first two conditions are checked by the fusermount
program before doing the mount. This has the nice feature, that it's
totally useless. Here's why:
- user creates /tmp/mydir
- user starts fusermount
- user removes /tmp/mydir just after fusermount checked that it is OK
- user creates symlink: ln -s / /tmp/mydir
- fusermount actually mounts user's filesystem on '/'
- this is bad :(
So to make this secure, the checks must be done by the kernel. And so
there is a patch (patch/ms_permission.patch) which does exactly this.
This is against 2.4.14, but applies to some earlier kernels (not too
much earlier though), and possibly some later (I couldn't know, could
I?).
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