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@example
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@c man begin SYNOPSIS
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usage: virtfs-proxy-helper options
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@c man end
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@end example
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@c man begin DESCRIPTION
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@table @description
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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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1) 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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2) Running QEMU with root privilege could be a security issue.
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To overcome above issues, following approach is used: A new filesytem
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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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Proxy helper is designed so that it can drop the root privilege with
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retaining capbilities needed for doing filesystem operations only.
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@end table
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@c man end
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@c man begin OPTIONS
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The following options are supported:
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@table @option
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@item -h
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@findex -h
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Display help and exit
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@item -p|--path path
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Path to export for proxy filesystem driver
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@item -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 -f|--fd
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@item -n|--nodaemon
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Run as a normal program. By default program will run in daemon mode
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@end table
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@c man end
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@setfilename virtfs-proxy-helper
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@settitle QEMU 9p virtfs proxy filesystem helper
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@c man begin AUTHOR
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M. Mohan Kumar
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@c man end