plucky (1) virtfs-proxy-helper.1.gz

Provided by: qemu-system-common_9.0.2+ds-4ubuntu9_amd64 bug

NAME
       virtfs-proxy-helper - QEMU 9p virtfs proxy filesystem helper


SYNOPSIS
       virtfs-proxy-helper [OPTIONS]


DESCRIPTION
       NOTE:  The 9p 'proxy' backend is deprecated (since QEMU 8.1) and will be removed, along with this daemon,
       in a future version of QEMU!

       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:

       • TOCTTOU  vulnerability:  Following symbolic links in the server could provide access to files beyond 9p
         export path.

       • Running QEMU with root privilege could be a security issue.

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

       The proxy helper is designed so that it can drop root privileges except for the capabilities  needed  for
       doing filesystem operations.


OPTIONS
       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 this option.

       -s, --socket SOCKET_FILE
              Creates named socket file for communicating with qemu proxy fs driver

       -u, --uid UID
              uid to give access to named socket file; used in combination with -g.

       -g, --gid GID
              gid to give access to named socket file; used in combination with -u.

       -n, --nodaemon
              Run as a normal program. By default program will run in daemon mode


AUTHOR
       M. Mohan Kumar


       2024, The QEMU Project Developers