mirror of
https://github.com/trapexit/mergerfs.git
synced 2024-12-11 19:53:39 +08:00
109 lines
4.0 KiB
Markdown
109 lines
4.0 KiB
Markdown
|
libfuse
|
||
|
|
=======
|
||
|
|
|
||
|
|
Warning: unresolved security issue
|
||
|
|
----------------------------------
|
||
|
|
|
||
|
|
Be aware that FUSE has an unresolved security bug
|
||
|
|
([bug #15](https://github.com/libfuse/libfuse/issues/15)): the
|
||
|
|
permission check for accessing a cached directory is only done once
|
||
|
|
when the directory entry is first loaded into the cache. Subsequent
|
||
|
|
accesses will re-use the results of the first check, even if the
|
||
|
|
directory permissions have since changed, and even if the subsequent
|
||
|
|
access is made by a different user.
|
||
|
|
|
||
|
|
This bug needs to be fixed in the Linux kernel and has been known
|
||
|
|
since 2006 but unfortunately no fix has been applied yet. If you
|
||
|
|
depend on correct permission handling for FUSE file systems, the only
|
||
|
|
workaround is to completely disable caching of directory
|
||
|
|
entries. Alternatively, the severity of the bug can be somewhat
|
||
|
|
reduced by not using the `allow_other` mount option.
|
||
|
|
|
||
|
|
|
||
|
|
About
|
||
|
|
-----
|
||
|
|
|
||
|
|
FUSE (Filesystem in Userspace) is an interface for userspace programs
|
||
|
|
to export a filesystem to the Linux kernel. The FUSE project consists
|
||
|
|
of two components: the *fuse* kernel module (maintained in the regular
|
||
|
|
kernel repositories) and the *libfuse* userspace library (maintained
|
||
|
|
in this repository). libfuse provides the reference implementation
|
||
|
|
for communicating with the FUSE kernel module.
|
||
|
|
|
||
|
|
A FUSE file system is typically implemented as a standalone
|
||
|
|
application that links with libfuse. libfuse provides functions to
|
||
|
|
mount the file system, unmount it, read requests from the kernel, and
|
||
|
|
send responses back. libfuse offers two APIs: a "high-level",
|
||
|
|
synchronous API, and a "low-level" asynchronous API. In both cases,
|
||
|
|
incoming requests from the kernel are passed to the main program using
|
||
|
|
callbacks. When using the high-level API, the callbacks may work with
|
||
|
|
file names and paths instead of inodes, and processing of a request
|
||
|
|
finishes when the callback function returns. When using the low-level
|
||
|
|
API, the callbacks must work with inodes and responses must be sent
|
||
|
|
explicitly using a separate set of API functions.
|
||
|
|
|
||
|
|
|
||
|
|
Installation
|
||
|
|
------------
|
||
|
|
|
||
|
|
./configure
|
||
|
|
make -j8
|
||
|
|
make install
|
||
|
|
|
||
|
|
You may also need to add `/usr/local/lib` to `/etc/ld.so.conf` and/or
|
||
|
|
run *ldconfig*. If you're building from the git repository (instead of
|
||
|
|
using a release tarball), you also need to run `./makeconf.sh` to
|
||
|
|
create the `configure` script.
|
||
|
|
|
||
|
|
You'll also need a fuse kernel module (Linux kernels 2.6.14 or later
|
||
|
|
contain FUSE support).
|
||
|
|
|
||
|
|
For more details see the file `INSTALL`
|
||
|
|
|
||
|
|
Security implications
|
||
|
|
---------------------
|
||
|
|
|
||
|
|
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, in order to prevent Bad User from
|
||
|
|
doing nasty things. 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)
|
||
|
|
|
||
|
|
- No other user (including root) can access the contents of the
|
||
|
|
mounted filesystem (though this can be relaxed by allowing the use
|
||
|
|
of the `allow_other` and `allow_root` mount options in `fuse.conf`)
|
||
|
|
|
||
|
|
|
||
|
|
Building your own filesystem
|
||
|
|
------------------------------
|
||
|
|
|
||
|
|
FUSE comes with several example file systems in the `examples`
|
||
|
|
directory. For example, the *fusexmp* example mirrors the contents of
|
||
|
|
the root directory under the mountpoint. Start from there and adapt
|
||
|
|
the code!
|
||
|
|
|
||
|
|
The documentation of the API functions and necessary callbacks is
|
||
|
|
mostly contained in the files `include/fuse.h` (for the high-level
|
||
|
|
API) and `include/fuse_lowlevel.h` (for the low-level API). An
|
||
|
|
autogenerated html version of the API is available in the `doc/html`
|
||
|
|
directory and at http://libfuse.github.io/doxygen.
|
||
|
|
|
||
|
|
|
||
|
|
Getting Help
|
||
|
|
------------
|
||
|
|
|
||
|
|
If you need help, please ask on the <fuse-devel@lists.sourceforge.net>
|
||
|
|
mailing list (subscribe at
|
||
|
|
https://lists.sourceforge.net/lists/listinfo/fuse-devel).
|
||
|
|
|
||
|
|
Please report any bugs on the GitHub issue tracker at
|
||
|
|
https://github.com/libfuse/main/issues.
|
||
|
|
|