root / fsdev / virtfs-proxy-helper.texi @ a2d8f1be
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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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|
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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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|
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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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|
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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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|
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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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|
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@setfilename virtfs-proxy-helper |
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@settitle QEMU 9p virtfs proxy filesystem helper |
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|
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@c man begin AUTHOR |
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M. Mohan Kumar |
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@c man end |