71d72ececa
As recent CVE-2023-2861 (fixed by f6b0de53fb) once again showed, the 9p
'proxy' fs driver is in bad shape. Using the 'proxy' backend was already
discouraged for safety reasons before and we recommended to use the
'local' backend (preferably in conjunction with its 'mapped' security
model) instead, but now it is time to officially deprecate the 'proxy'
backend.
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <E1qDkmw-0007M1-8f@lizzy.crudebyte.com>
76 lines
2.3 KiB
ReStructuredText
76 lines
2.3 KiB
ReStructuredText
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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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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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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