|
1 |
@example
|
|
2 |
@c man begin SYNOPSIS
|
|
3 |
usage: virtfs-proxy-helper options
|
|
4 |
@c man end
|
|
5 |
@end example
|
|
6 |
|
|
7 |
@c man begin DESCRIPTION
|
|
8 |
@table @description
|
|
9 |
Pass-through security model in QEMU 9p server needs root privilege to do
|
|
10 |
few file operations (like chown, chmod to any mode/uid:gid). There are two
|
|
11 |
issues in pass-through security model
|
|
12 |
|
|
13 |
1) TOCTTOU vulnerability: Following symbolic links in the server could
|
|
14 |
provide access to files beyond 9p export path.
|
|
15 |
|
|
16 |
2) Running QEMU with root privilege could be a security issue.
|
|
17 |
|
|
18 |
To overcome above issues, following approach is used: A new filesytem
|
|
19 |
type 'proxy' is introduced. Proxy FS uses chroot + socket combination
|
|
20 |
for securing the vulnerability known with following symbolic links.
|
|
21 |
Intention of adding a new filesystem type is to allow qemu to run
|
|
22 |
in non-root mode, but doing privileged operations using socket IO.
|
|
23 |
|
|
24 |
Proxy helper(a stand alone binary part of qemu) is invoked with
|
|
25 |
root privileges. Proxy helper chroots into 9p export path and creates
|
|
26 |
a socket pair or a named socket based on the command line parameter.
|
|
27 |
Qemu and proxy helper communicate using this socket. QEMU proxy fs
|
|
28 |
driver sends filesystem request to proxy helper and receives the
|
|
29 |
response from it.
|
|
30 |
|
|
31 |
Proxy helper is designed so that it can drop the root privilege with
|
|
32 |
retaining capbilities needed for doing filesystem operations only.
|
|
33 |
|
|
34 |
@end table
|
|
35 |
@c man end
|
|
36 |
|
|
37 |
@c man begin OPTIONS
|
|
38 |
The following options are supported:
|
|
39 |
@table @option
|
|
40 |
@item -h
|
|
41 |
@findex -h
|
|
42 |
Display help and exit
|
|
43 |
@item -p|--path path
|
|
44 |
Path to export for proxy filesystem driver
|
|
45 |
@item -f|--fd socket-id
|
|
46 |
Use given file descriptor as socket descriptor for communicating with
|
|
47 |
qemu proxy fs drier. Usually a helper like libvirt will create
|
|
48 |
socketpair and pass one of the fds as parameter to -f|--fd
|
|
49 |
@item -n|--nodaemon
|
|
50 |
Run as a normal program. By default program will run in daemon mode
|
|
51 |
@end table
|
|
52 |
@c man end
|
|
53 |
|
|
54 |
@setfilename virtfs-proxy-helper
|
|
55 |
@settitle QEMU 9p virtfs proxy filesystem helper
|
|
56 |
|
|
57 |
@c man begin AUTHOR
|
|
58 |
M. Mohan Kumar
|
|
59 |
@c man end
|