2020-01-24 19:26:06 +03:00
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QEMU 9p virtfs proxy filesystem helper
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======================================
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Synopsis
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--------
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**virtfs-proxy-helper** [*OPTIONS*]
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Description
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-----------
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2023-06-26 14:49:06 +03:00
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NOTE: The 9p 'proxy' backend is deprecated (since QEMU 8.1) and will be
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removed, along with this daemon, in a future version of QEMU!
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2020-01-24 19:26:06 +03:00
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Pass-through security model in QEMU 9p server needs root privilege to do
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few file operations (like chown, chmod to any mode/uid:gid). There are two
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issues in pass-through security model:
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- TOCTTOU vulnerability: Following symbolic links in the server could
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provide access to files beyond 9p export path.
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- Running QEMU with root privilege could be a security issue.
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To overcome above issues, following approach is used: A new filesystem
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type 'proxy' is introduced. Proxy FS uses chroot + socket combination
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for securing the vulnerability known with following symbolic links.
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Intention of adding a new filesystem type is to allow qemu to run
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in non-root mode, but doing privileged operations using socket IO.
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Proxy helper (a stand alone binary part of qemu) is invoked with
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root privileges. Proxy helper chroots into 9p export path and creates
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a socket pair or a named socket based on the command line parameter.
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QEMU and proxy helper communicate using this socket. QEMU proxy fs
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driver sends filesystem request to proxy helper and receives the
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response from it.
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The proxy helper is designed so that it can drop root privileges except
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for the capabilities needed for doing filesystem operations.
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Options
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-------
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The following options are supported:
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.. program:: virtfs-proxy-helper
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.. option:: -h
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Display help and exit
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.. option:: -p, --path PATH
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Path to export for proxy filesystem driver
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.. option:: -f, --fd SOCKET_ID
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Use given file descriptor as socket descriptor for communicating with
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qemu proxy fs drier. Usually a helper like libvirt will create
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socketpair and pass one of the fds as parameter to this option.
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.. option:: -s, --socket SOCKET_FILE
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Creates named socket file for communicating with qemu proxy fs driver
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.. option:: -u, --uid UID
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uid to give access to named socket file; used in combination with -g.
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.. option:: -g, --gid GID
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gid to give access to named socket file; used in combination with -u.
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.. option:: -n, --nodaemon
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Run as a normal program. By default program will run in daemon mode
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