virtfs-proxy-helper (1)
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NAME
virtfs-proxy-helper - QEMU 9p virtfs proxy filesystem helperSYNOPSIS
virtfs-proxy-helper optionsDESCRIPTION
-
Pass-through security model in QEMU9p 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)
TOCTTOUvulnerability: Following symbolic links in the server could provide access to files beyond 9p export path.2) Running
QEMUwith root privilege could be a security issue.To overcome above issues, following approach is used: A new filesystem type 'proxy' is introduced. Proxy
FSuses 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 socketIO.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.
QEMUand proxy helper communicate using this socket.QEMUproxy 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.
OPTIONS
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 driver
- -u|--uid uid -g|--gid gid
- uid:gid combination to give access to named socket file
- -n|--nodaemon
- Run as a normal program. By default program will run in daemon mode