virtfs-proxy-helper (1)

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NAME

virtfs-proxy-helper - QEMU 9p virtfs proxy filesystem helper

SYNOPSIS

virtfs-proxy-helper options

DESCRIPTION

Pass-through security model in

QEMU

9p 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)

TOCTTOU

vulnerability: Following symbolic links in the server could provide access to files beyond 9p export path.

2) Running

QEMU

with root privilege could be a security issue.

To overcome above issues, following approach is used: A new filesystem type 'proxy' is introduced. Proxy

FS

uses 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 socket

IO.

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.

QEMU

and proxy helper communicate using this socket.

QEMU

proxy 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

AUTHOR

M. Mohan Kumar