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

       2024, The QEMU Project Developers