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@@ -0,0 +1,101 @@ +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?). + |