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1@example
2@c man begin SYNOPSIS
3usage: virtfs-proxy-helper options
4@c man end
5@end example
6
7@c man begin DESCRIPTION
8@table @description
9Pass-through security model in QEMU 9p server needs root privilege to do
10few file operations (like chown, chmod to any mode/uid:gid). There are two
11issues in pass-through security model
12
131) TOCTTOU vulnerability: Following symbolic links in the server could
14provide access to files beyond 9p export path.
15
162) Running QEMU with root privilege could be a security issue.
17
18To overcome above issues, following approach is used: A new filesytem
19type 'proxy' is introduced. Proxy FS uses chroot + socket combination
20for securing the vulnerability known with following symbolic links.
21Intention of adding a new filesystem type is to allow qemu to run
22in non-root mode, but doing privileged operations using socket IO.
23
24Proxy helper(a stand alone binary part of qemu) is invoked with
25root privileges. Proxy helper chroots into 9p export path and creates
26a socket pair or a named socket based on the command line parameter.
071c9394 27QEMU and proxy helper communicate using this socket. QEMU proxy fs
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28driver sends filesystem request to proxy helper and receives the
29response from it.
30
31Proxy helper is designed so that it can drop the root privilege with
32retaining capbilities needed for doing filesystem operations only.
33
34@end table
35@c man end
36
37@c man begin OPTIONS
38The following options are supported:
39@table @option
40@item -h
41@findex -h
42Display help and exit
43@item -p|--path path
44Path to export for proxy filesystem driver
45@item -f|--fd socket-id
46Use given file descriptor as socket descriptor for communicating with
47qemu proxy fs drier. Usually a helper like libvirt will create
48socketpair and pass one of the fds as parameter to -f|--fd
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49@item -s|--socket socket-file
50Creates named socket file for communicating with qemu proxy fs driver
51@item -u|--uid uid -g|--gid gid
52uid:gid combination to give access to named socket file
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53@item -n|--nodaemon
54Run as a normal program. By default program will run in daemon mode
55@end table
56@c man end
57
58@setfilename virtfs-proxy-helper
59@settitle QEMU 9p virtfs proxy filesystem helper
60
61@c man begin AUTHOR
62M. Mohan Kumar
63@c man end