VIRTFS-PROXY-HELPER.1(1)                              VIRTFS-PROXY-HELPER.1(1)

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

       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
           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.

       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

       -u|--uid uid -g|--gid gid
           uid:gid combination to give access to named socket file

           Run as a normal program. By default program will run in daemon mode

       M. Mohan Kumar

                                  2018-01-11          VIRTFS-PROXY-HELPER.1(1)

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