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

COPYRIGHT

       2025, The QEMU Project Developers

8.2.2                                             Mar 13, 2025                            VIRTFS-PROXY-HELPER(1)