Provided by: qemu-system-common_2.0.0~rc1+dfsg-0ubuntu3_amd64
virtfs-proxy-helper - QEMU 9p virtfs proxy filesystem helper
usage: virtfs-proxy-helper options
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.
The following options are supported: -h Display help and exit -p|--path path Path to export for proxy filesystem driver -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 -s|--socket socket-file Creates named socket file for communicating with qemu proxy fs driver -u|--uid uid -g|--gid gid uid:gid combination to give access to named socket file -n|--nodaemon Run as a normal program. By default program will run in daemon mode
M. Mohan Kumar 2014-04-09 VIRTFS-PROXY-HELPER(1)