NAME

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

SYNOPSIS

       virtfs-proxy-helper [OPTIONS]

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:

       • 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

       2024, The QEMU Project Developers