qemu/qemu-nbd.texi
Daniel P. Berrange b25e12daff qemu-nbd: add support for authorization of TLS clients
Currently any client which can complete the TLS handshake is able to use
the NBD server. The server admin can turn on the 'verify-peer' option
for the x509 creds to require the client to provide a x509 certificate.
This means the client will have to acquire a certificate from the CA
before they are permitted to use the NBD server. This is still a fairly
low bar to cross.

This adds a '--tls-authz OBJECT-ID' option to the qemu-nbd command which
takes the ID of a previously added 'QAuthZ' object instance. This will
be used to validate the client's x509 distinguished name. Clients
failing the authorization check will not be permitted to use the NBD
server.

For example to setup authorization that only allows connection from a client
whose x509 certificate distinguished name is

   CN=laptop.example.com,O=Example Org,L=London,ST=London,C=GB

escape the commas in the name and use:

  qemu-nbd --object tls-creds-x509,id=tls0,dir=/home/berrange/qemutls,\
                    endpoint=server,verify-peer=yes \
           --object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,\
                     O=Example Org,,L=London,,ST=London,,C=GB' \
           --tls-creds tls0 \
           --tls-authz authz0 \
	   ....other qemu-nbd args...

NB: a real shell command line would not have leading whitespace after
the line continuation, it is just included here for clarity.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <20190227162035.18543-2-berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: split long line in --help text, tweak 233 to show that whitespace
after ,, in identity= portion is actually okay]
Signed-off-by: Eric Blake <eblake@redhat.com>
2019-03-06 11:05:27 -06:00

213 lines
7.7 KiB
Plaintext

@example
@c man begin SYNOPSIS
@command{qemu-nbd} [OPTION]... @var{filename}
@command{qemu-nbd} @option{-L} [OPTION]...
@command{qemu-nbd} @option{-d} @var{dev}
@c man end
@end example
@c man begin DESCRIPTION
Export a QEMU disk image using the NBD protocol.
Other uses:
@itemize
@item
Bind a /dev/nbdX block device to a QEMU server (on Linux).
@item
As a client to query exports of a remote NBD server.
@end itemize
@c man end
@c man begin OPTIONS
@var{filename} is a disk image filename, or a set of block
driver options if @option{--image-opts} is specified.
@var{dev} is an NBD device.
@table @option
@item --object type,id=@var{id},...props...
Define a new instance of the @var{type} object class identified by @var{id}.
See the @code{qemu(1)} manual page for full details of the properties
supported. The common object types that it makes sense to define are the
@code{secret} object, which is used to supply passwords and/or encryption
keys, and the @code{tls-creds} object, which is used to supply TLS
credentials for the qemu-nbd server or client.
@item -p, --port=@var{port}
The TCP port to listen on as a server, or connect to as a client
(default @samp{10809}).
@item -o, --offset=@var{offset}
The offset into the image.
@item -b, --bind=@var{iface}
The interface to bind to as a server, or connect to as a client
(default @samp{0.0.0.0}).
@item -k, --socket=@var{path}
Use a unix socket with path @var{path}.
@item --image-opts
Treat @var{filename} as a set of image options, instead of a plain
filename. If this flag is specified, the @var{-f} flag should
not be used, instead the '@code{format=}' option should be set.
@item -f, --format=@var{fmt}
Force the use of the block driver for format @var{fmt} instead of
auto-detecting.
@item -r, --read-only
Export the disk as read-only.
@item -P, --partition=@var{num}
Deprecated: Only expose MBR partition @var{num}. Understands physical
partitions 1-4 and logical partition 5. New code should instead use
@option{--image-opts} with the raw driver wrapping a subset of the
original image.
@item -B, --bitmap=@var{name}
If @var{filename} has a qcow2 persistent bitmap @var{name}, expose
that bitmap via the ``qemu:dirty-bitmap:@var{name}'' context
accessible through NBD_OPT_SET_META_CONTEXT.
@item -s, --snapshot
Use @var{filename} as an external snapshot, create a temporary
file with backing_file=@var{filename}, redirect the write to
the temporary one.
@item -l, --load-snapshot=@var{snapshot_param}
Load an internal snapshot inside @var{filename} and export it
as an read-only device, @var{snapshot_param} format is
'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'
@item -n, --nocache
@itemx --cache=@var{cache}
The cache mode to be used with the file. See the documentation of
the emulator's @code{-drive cache=...} option for allowed values.
@item --aio=@var{aio}
Set the asynchronous I/O mode between @samp{threads} (the default)
and @samp{native} (Linux only).
@item --discard=@var{discard}
Control whether @dfn{discard} (also known as @dfn{trim} or @dfn{unmap})
requests are ignored or passed to the filesystem. @var{discard} is one of
@samp{ignore} (or @samp{off}), @samp{unmap} (or @samp{on}). The default is
@samp{ignore}.
@item --detect-zeroes=@var{detect-zeroes}
Control the automatic conversion of plain zero writes by the OS to
driver-specific optimized zero write commands. @var{detect-zeroes} is one of
@samp{off}, @samp{on} or @samp{unmap}. @samp{unmap}
converts a zero write to an unmap operation and can only be used if
@var{discard} is set to @samp{unmap}. The default is @samp{off}.
@item -c, --connect=@var{dev}
Connect @var{filename} to NBD device @var{dev} (Linux only).
@item -d, --disconnect
Disconnect the device @var{dev} (Linux only).
@item -e, --shared=@var{num}
Allow up to @var{num} clients to share the device (default
@samp{1}). Safe for readers, but for now, consistency is not
guaranteed between multiple writers.
@item -t, --persistent
Don't exit on the last connection.
@item -x, --export-name=@var{name}
Set the NBD volume export name (default of a zero-length string).
@item -D, --description=@var{description}
Set the NBD volume export description, as a human-readable
string.
@item -L, --list
Connect as a client and list all details about the exports exposed by
a remote NBD server. This enables list mode, and is incompatible
with options that change behavior related to a specific export (such as
@option{--export-name}, @option{--offset}, ...).
@item --tls-creds=ID
Enable mandatory TLS encryption for the server by setting the ID
of the TLS credentials object previously created with the --object
option; or provide the credentials needed for connecting as a client
in list mode.
@item --fork
Fork off the server process and exit the parent once the server is running.
@item --tls-authz=ID
Specify the ID of a qauthz object previously created with the
--object option. This will be used to authorize connecting users
against their x509 distinguished name.
@item -v, --verbose
Display extra debugging information.
@item -h, --help
Display this help and exit.
@item -V, --version
Display version information and exit.
@item -T, --trace [[enable=]@var{pattern}][,events=@var{file}][,file=@var{file}]
@findex --trace
@include qemu-option-trace.texi
@end table
@c man end
@c man begin EXAMPLES
Start a server listening on port 10809 that exposes only the
guest-visible contents of a qcow2 file, with no TLS encryption, and
with the default export name (an empty string). The command is
one-shot, and will block until the first successful client
disconnects:
@example
qemu-nbd -f qcow2 file.qcow2
@end example
Start a long-running server listening with encryption on port 10810,
and whitelist clients with a specific X.509 certificate to connect to
a 1 megabyte subset of a raw file, using the export name 'subset':
@example
qemu-nbd \
--object tls-creds-x509,id=tls0,endpoint=server,dir=/path/to/qemutls \
--object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,\
O=Example Org,,L=London,,ST=London,,C=GB' \
--tls-creds tls0 --tls-authz auth0 \
-t -x subset -p 10810 \
--image-opts driver=raw,offset=1M,size=1M,file.driver=file,file.filename=file.raw
@end example
Serve a read-only copy of just the first MBR partition of a guest
image over a Unix socket with as many as 5 simultaneous readers, with
a persistent process forked as a daemon:
@example
qemu-nbd --fork --persistent --shared=5 --socket=/path/to/sock \
--partition=1 --read-only --format=qcow2 file.qcow2
@end example
Expose the guest-visible contents of a qcow2 file via a block device
/dev/nbd0 (and possibly creating /dev/nbd0p1 and friends for
partitions found within), then disconnect the device when done.
Access to bind qemu-nbd to an /dev/nbd device generally requires root
privileges, and may also require the execution of @code{modprobe nbd}
to enable the kernel NBD client module. @emph{CAUTION}: Do not use
this method to mount filesystems from an untrusted guest image - a
malicious guest may have prepared the image to attempt to trigger
kernel bugs in partition probing or file system mounting.
@example
qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2
qemu-nbd -d /dev/nbd0
@end example
Query a remote server to see details about what export(s) it is
serving on port 10809, and authenticating via PSK:
@example
qemu-nbd \
--object tls-creds-psk,id=tls0,dir=/tmp/keys,username=eblake,endpoint=client \
--tls-creds tls0 -L -b remote.example.com
@end example
@c man end
@ignore
@setfilename qemu-nbd
@settitle QEMU Disk Network Block Device Server
@c man begin AUTHOR
Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
@c man end
@c man begin SEEALSO
qemu(1), qemu-img(1)
@c man end
@end ignore