Archipelago » qemu

@example

@c man begin SYNOPSIS

usage: virtfs-proxy-helper options

@c man end

@end example

@c man begin DESCRIPTION

@table @description

Pass-through security model in QEMU 9p server needs root privilege to do

few file operations (like chown, chmod to any mode/uid:gid).  There are two

issues in pass-through security model

1) TOCTTOU vulnerability: Following symbolic links in the server could

provide access to files beyond 9p export path.

2) Running QEMU with root privilege could be a security issue.

To overcome above issues, following approach is used: A new filesytem

type 'proxy' is introduced. Proxy FS uses chroot + socket combination

for securing the vulnerability known with following symbolic links.

Intention of adding a new filesystem type is to allow qemu to run

in non-root mode, but doing privileged operations using socket IO.

Proxy helper(a stand alone binary part of qemu) is invoked with

root privileges. Proxy helper chroots into 9p export path and creates

a socket pair or a named socket based on the command line parameter.

QEMU and proxy helper communicate using this socket. QEMU proxy fs

driver sends filesystem request to proxy helper and receives the

response from it.

Proxy helper is designed so that it can drop the root privilege with

retaining capbilities needed for doing filesystem operations only.

@end table

@c man end

@c man begin OPTIONS

The following options are supported:

@table @option

@item -h

@findex -h

Display help and exit

@item -p|--path path

Path to export for proxy filesystem driver

@item -f|--fd socket-id

Use given file descriptor as socket descriptor for communicating with

qemu proxy fs drier. Usually a helper like libvirt will create

socketpair and pass one of the fds as parameter to -f|--fd

@item -s|--socket socket-file

Creates named socket file for communicating with qemu proxy fs driver

@item -u|--uid uid -g|--gid gid

uid:gid combination to give access to named socket file

@item -n|--nodaemon

Run as a normal program. By default program will run in daemon mode

@end table

@c man end

@setfilename virtfs-proxy-helper

@settitle QEMU 9p virtfs proxy filesystem helper

@c man begin AUTHOR

M. Mohan Kumar

@c man end