Commit 2f9606b3 authored by aliguori's avatar aliguori

Add SASL authentication support ("Daniel P. Berrange")

This patch adds the new SASL authentication protocol to the VNC server.

It is enabled by setting the 'sasl' flag when launching VNC. SASL can
optionally provide encryption via its SSF layer, if a suitable mechanism
is configured (eg, GSSAPI/Kerberos, or Digest-MD5).  If an SSF layer is
not available, then it should be combined with the x509 VNC authentication
protocol which provides encryption.

eg, if using GSSAPI

   qemu -vnc localhost:1,sasl

eg if using  TLS/x509 for encryption

   qemu -vnc localhost:1,sasl,tls,x509


By default the Cyrus SASL library will look for its configuration in
the file /etc/sasl2/qemu.conf.  For non-root users, this can be overridden
by setting the SASL_CONF_PATH environment variable, eg to make it look in
$HOME/.sasl2.  NB unprivileged users may not have access to the full range
of SASL mechanisms, since some of them require some administrative privileges
to configure. The patch includes an example SASL configuration file which
illustrates config for GSSAPI and Digest-MD5, though it should be noted that
the latter is not really considered secure any more.

Most of the SASL authentication code is located in a separate source file,
vnc-auth-sasl.c.  The main vnc.c file only contains minimal integration
glue, specifically parsing of command line flags / setup, and calls to
start the SASL auth process, to do encoding/decoding for data.

There are several possible stacks for reading & writing of data, depending
on the combo of VNC authentication methods in use

 - Clear.    read/write straight to socket
 - TLS.      read/write via GNUTLS helpers
 - SASL.     encode/decode via SASL SSF layer, then read/write to socket
 - SASL+TLS. encode/decode via SASL SSF layer, then read/write via GNUTLS

Hence, the vnc_client_read & vnc_client_write methods have been refactored
a little.

   vnc_client_read:  main entry point for reading, calls either

       - vnc_client_read_plain   reading, with no intermediate decoding
       - vnc_client_read_sasl    reading, with SASL SSF decoding

   These two methods, then call vnc_client_read_buf(). This decides
   whether to write to the socket directly or write via GNUTLS.

The situation is the same for writing data. More extensive comments
have been added in the code / patch. The vnc_client_read_sasl and
vnc_client_write_sasl method implementations live in the separate
vnc-auth-sasl.c file.

The state required for the SASL auth mechanism is kept in a separate
VncStateSASL struct, defined in vnc-auth-sasl.h and included in the
main VncState.

The configure script probes for SASL and automatically enables it
if found, unless --disable-vnc-sasl was given to override it.


 Makefile            |    7 
 Makefile.target     |    5 
 b/qemu.sasl         |   34 ++
 b/vnc-auth-sasl.c   |  626 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 b/vnc-auth-sasl.h   |   67 +++++
 configure           |   34 ++
 qemu-doc.texi       |   97 ++++++++
 vnc-auth-vencrypt.c |   12 
 vnc.c               |  249 ++++++++++++++++++--
 vnc.h               |   31 ++
 10 files changed, 1129 insertions(+), 33 deletions(-)
Signed-off-by: default avatarDaniel P. Berrange <berrange@redhat.com>
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6724 c046a42c-6fe2-441c-8c8c-71466251a162
parent 5fb6c7a8
......@@ -148,6 +148,9 @@ OBJS+=vnc.o d3des.o
ifdef CONFIG_VNC_TLS
OBJS+=vnc-tls.o vnc-auth-vencrypt.o
endif
ifdef CONFIG_VNC_SASL
OBJS+=vnc-auth-sasl.o
endif
ifdef CONFIG_COCOA
OBJS+=cocoa.o
......@@ -171,7 +174,7 @@ sdl.o: sdl.c keymaps.h sdl_keysym.h
sdl.o audio/sdlaudio.o: CFLAGS += $(SDL_CFLAGS)
vnc.h: vnc-tls.h vnc-auth-vencrypt.h keymaps.h
vnc.h: vnc-tls.h vnc-auth-vencrypt.h vnc-auth-sasl.h keymaps.h
vnc.o: vnc.c vnc.h vnc_keysym.h vnchextile.h d3des.c d3des.h
......@@ -181,6 +184,8 @@ vnc-tls.o: vnc-tls.c vnc.h
vnc-auth-vencrypt.o: vnc-auth-vencrypt.c vnc.h
vnc-auth-sasl.o: vnc-auth-sasl.c vnc.h
curses.o: curses.c keymaps.h curses_keys.h
bt-host.o: CFLAGS += $(CONFIG_BLUEZ_CFLAGS)
......
......@@ -554,6 +554,11 @@ CPPFLAGS += $(CONFIG_VNC_TLS_CFLAGS)
LIBS += $(CONFIG_VNC_TLS_LIBS)
endif
ifdef CONFIG_VNC_SASL
CPPFLAGS += $(CONFIG_VNC_SASL_CFLAGS)
LIBS += $(CONFIG_VNC_SASL_LIBS)
endif
ifdef CONFIG_BLUEZ
LIBS += $(CONFIG_BLUEZ_LIBS)
endif
......
......@@ -164,6 +164,7 @@ fmod_lib=""
fmod_inc=""
oss_lib=""
vnc_tls="yes"
vnc_sasl="yes"
bsd="no"
linux="no"
solaris="no"
......@@ -388,6 +389,8 @@ for opt do
;;
--disable-vnc-tls) vnc_tls="no"
;;
--disable-vnc-sasl) vnc_sasl="no"
;;
--disable-slirp) slirp="no"
;;
--disable-vde) vde="no"
......@@ -545,6 +548,7 @@ echo " Available cards: $audio_possible_cards"
echo " --enable-mixemu enable mixer emulation"
echo " --disable-brlapi disable BrlAPI"
echo " --disable-vnc-tls disable TLS encryption for VNC server"
echo " --disable-vnc-sasl disable SASL encryption for VNC server"
echo " --disable-curses disable curses output"
echo " --disable-bluez disable bluez stack connectivity"
echo " --disable-kvm disable KVM acceleration support"
......@@ -838,6 +842,25 @@ EOF
fi
fi
##########################################
# VNC SASL detection
if test "$vnc_sasl" = "yes" ; then
cat > $TMPC <<EOF
#include <sasl/sasl.h>
#include <stdio.h>
int main(void) { sasl_server_init(NULL, "qemu"); return 0; }
EOF
# Assuming Cyrus-SASL installed in /usr prefix
vnc_sasl_cflags=""
vnc_sasl_libs="-lsasl2"
if $cc $ARCH_CFLAGS -o $TMPE ${OS_CFLAGS} $vnc_sasl_cflags $TMPC \
$vnc_sasl_libs 2> /dev/null ; then
:
else
vnc_sasl="no"
fi
fi
##########################################
# vde libraries probe
if test "$vde" = "yes" ; then
......@@ -1146,6 +1169,11 @@ if test "$vnc_tls" = "yes" ; then
echo " TLS CFLAGS $vnc_tls_cflags"
echo " TLS LIBS $vnc_tls_libs"
fi
echo "VNC SASL support $vnc_sasl"
if test "$vnc_sasl" = "yes" ; then
echo " SASL CFLAGS $vnc_sasl_cflags"
echo " SASL LIBS $vnc_sasl_libs"
fi
if test -n "$sparc_cpu"; then
echo "Target Sparc Arch $sparc_cpu"
fi
......@@ -1387,6 +1415,12 @@ if test "$vnc_tls" = "yes" ; then
echo "CONFIG_VNC_TLS_LIBS=$vnc_tls_libs" >> $config_mak
echo "#define CONFIG_VNC_TLS 1" >> $config_h
fi
if test "$vnc_sasl" = "yes" ; then
echo "CONFIG_VNC_SASL=yes" >> $config_mak
echo "CONFIG_VNC_SASL_CFLAGS=$vnc_sasl_cflags" >> $config_mak
echo "CONFIG_VNC_SASL_LIBS=$vnc_sasl_libs" >> $config_mak
echo "#define CONFIG_VNC_SASL 1" >> $config_h
fi
qemu_version=`head $source_path/VERSION`
echo "VERSION=$qemu_version" >>$config_mak
echo "#define QEMU_VERSION \"$qemu_version\"" >> $config_h
......
......@@ -616,6 +616,21 @@ path following this option specifies where the x509 certificates are to
be loaded from. See the @ref{vnc_security} section for details on generating
certificates.
@item sasl
Require that the client use SASL to authenticate with the VNC server.
The exact choice of authentication method used is controlled from the
system / user's SASL configuration file for the 'qemu' service. This
is typically found in /etc/sasl2/qemu.conf. If running QEMU as an
unprivileged user, an environment variable SASL_CONF_PATH can be used
to make it search alternate locations for the service config.
While some SASL auth methods can also provide data encryption (eg GSSAPI),
it is recommended that SASL always be combined with the 'tls' and
'x509' settings to enable use of SSL and server certificates. This
ensures a data encryption preventing compromise of authentication
credentials. See the @ref{vnc_security} section for details on using
SASL authentication.
@end table
@end table
......@@ -2061,7 +2076,10 @@ considerations depending on the deployment scenarios.
* vnc_sec_certificate::
* vnc_sec_certificate_verify::
* vnc_sec_certificate_pw::
* vnc_sec_sasl::
* vnc_sec_certificate_sasl::
* vnc_generate_cert::
* vnc_setup_sasl::
@end menu
@node vnc_sec_none
@subsection Without passwords
......@@ -2144,6 +2162,41 @@ Password: ********
(qemu)
@end example
@node vnc_sec_sasl
@subsection With SASL authentication
The SASL authentication method is a VNC extension, that provides an
easily extendable, pluggable authentication method. This allows for
integration with a wide range of authentication mechanisms, such as
PAM, GSSAPI/Kerberos, LDAP, SQL databases, one-time keys and more.
The strength of the authentication depends on the exact mechanism
configured. If the chosen mechanism also provides a SSF layer, then
it will encrypt the datastream as well.
Refer to the later docs on how to choose the exact SASL mechanism
used for authentication, but assuming use of one supporting SSF,
then QEMU can be launched with:
@example
qemu [...OPTIONS...] -vnc :1,sasl -monitor stdio
@end example
@node vnc_sec_certificate_sasl
@subsection With x509 certificates and SASL authentication
If the desired SASL authentication mechanism does not supported
SSF layers, then it is strongly advised to run it in combination
with TLS and x509 certificates. This provides securely encrypted
data stream, avoiding risk of compromising of the security
credentials. This can be enabled, by combining the 'sasl' option
with the aforementioned TLS + x509 options:
@example
qemu [...OPTIONS...] -vnc :1,tls,x509,sasl -monitor stdio
@end example
@node vnc_generate_cert
@subsection Generating certificates for VNC
......@@ -2255,6 +2308,50 @@ EOF
The @code{client-key.pem} and @code{client-cert.pem} files should now be securely
copied to the client for which they were generated.
@node vnc_setup_sasl
@subsection Configuring SASL mechanisms
The following documentation assumes use of the Cyrus SASL implementation on a
Linux host, but the principals should apply to any other SASL impl. When SASL
is enabled, the mechanism configuration will be loaded from system default
SASL service config /etc/sasl2/qemu.conf. If running QEMU as an
unprivileged user, an environment variable SASL_CONF_PATH can be used
to make it search alternate locations for the service config.
The default configuration might contain
@example
mech_list: digest-md5
sasldb_path: /etc/qemu/passwd.db
@end example
This says to use the 'Digest MD5' mechanism, which is similar to the HTTP
Digest-MD5 mechanism. The list of valid usernames & passwords is maintained
in the /etc/qemu/passwd.db file, and can be updated using the saslpasswd2
command. While this mechanism is easy to configure and use, it is not
considered secure by modern standards, so only suitable for developers /
ad-hoc testing.
A more serious deployment might use Kerberos, which is done with the 'gssapi'
mechanism
@example
mech_list: gssapi
keytab: /etc/qemu/krb5.tab
@end example
For this to work the administrator of your KDC must generate a Kerberos
principal for the server, with a name of 'qemu/somehost.example.com@@EXAMPLE.COM'
replacing 'somehost.example.com' with the fully qualified host name of the
machine running QEMU, and 'EXAMPLE.COM' with the Keberos Realm.
Other configurations will be left as an exercise for the reader. It should
be noted that only Digest-MD5 and GSSAPI provides a SSF layer for data
encryption. For all other mechanisms, VNC should always be configured to
use TLS and x509 certificates to protect security credentials from snooping.
@node gdb_usage
@section GDB usage
......
# If you want to use the non-TLS socket, then you *must* include
# the GSSAPI or DIGEST-MD5 mechanisms, because they are the only
# ones that can offer session encryption as well as authentication.
#
# If you're only using TLS, then you can turn on any mechanisms
# you like for authentication, because TLS provides the encryption
#
# Default to a simple username+password mechanism
# NB digest-md5 is no longer considered secure by current standards
mech_list: digest-md5
# Before you can use GSSAPI, you need a service principle on the
# KDC server for libvirt, and that to be exported to the keytab
# file listed below
#mech_list: gssapi
#
# You can also list many mechanisms at once, then the user can choose
# by adding '?auth=sasl.gssapi' to their libvirt URI, eg
# qemu+tcp://hostname/system?auth=sasl.gssapi
#mech_list: digest-md5 gssapi
# Some older builds of MIT kerberos on Linux ignore this option &
# instead need KRB5_KTNAME env var.
# For modern Linux, and other OS, this should be sufficient
keytab: /etc/qemu/krb5.tab
# If using digest-md5 for username/passwds, then this is the file
# containing the passwds. Use 'saslpasswd2 -a qemu [username]'
# to add entries, and 'sasldblistusers2 -a qemu' to browse it
sasldb_path: /etc/qemu/passwd.db
auxprop_plugin: sasldb
This diff is collapsed.
/*
* QEMU VNC display driver: SASL auth protocol
*
* Copyright (C) 2009 Red Hat, Inc
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#ifndef __QEMU_VNC_AUTH_SASL_H__
#define __QEMU_VNC_AUTH_SASL_H__
#include <sasl/sasl.h>
typedef struct VncStateSASL VncStateSASL;
struct VncStateSASL {
sasl_conn_t *conn;
/* If we want to negotiate an SSF layer with client */
int wantSSF :1;
/* If we are now running the SSF layer */
int runSSF :1;
/*
* If this is non-zero, then wait for that many bytes
* to be written plain, before switching to SSF encoding
* This allows the VNC auth result to finish being
* written in plain.
*/
unsigned int waitWriteSSF;
/*
* Buffering encoded data to allow more clear data
* to be stuffed onto the output buffer
*/
const uint8_t *encoded;
unsigned int encodedLength;
unsigned int encodedOffset;
char *username;
char *mechlist;
};
void vnc_sasl_client_cleanup(VncState *vs);
long vnc_client_read_sasl(VncState *vs);
long vnc_client_write_sasl(VncState *vs);
void start_auth_sasl(VncState *vs);
#endif /* __QEMU_VNC_AUTH_SASL_H__ */
This diff is collapsed.
......@@ -80,6 +80,10 @@ typedef struct VncDisplay VncDisplay;
#include "vnc-tls.h"
#include "vnc-auth-vencrypt.h"
#endif
#ifdef CONFIG_VNC_SASL
#include "vnc-auth-sasl.h"
#endif
struct VncDisplay
{
......@@ -119,10 +123,12 @@ struct VncState
int minor;
char challenge[VNC_AUTH_CHALLENGE_SIZE];
#ifdef CONFIG_VNC_TLS
VncStateTLS tls;
#endif
#ifdef CONFIG_VNC_SASL
VncStateSASL sasl;
#endif
Buffer output;
Buffer input;
......@@ -161,8 +167,9 @@ enum {
VNC_AUTH_RA2NE = 6,
VNC_AUTH_TIGHT = 16,
VNC_AUTH_ULTRA = 17,
VNC_AUTH_TLS = 18,
VNC_AUTH_VENCRYPT = 19
VNC_AUTH_TLS = 18, /* Supported in GTK-VNC & VINO */
VNC_AUTH_VENCRYPT = 19, /* Supported in GTK-VNC & VeNCrypt */
VNC_AUTH_SASL = 20, /* Supported in GTK-VNC & VINO */
};
enum {
......@@ -173,6 +180,8 @@ enum {
VNC_AUTH_VENCRYPT_X509NONE = 260,
VNC_AUTH_VENCRYPT_X509VNC = 261,
VNC_AUTH_VENCRYPT_X509PLAIN = 262,
VNC_AUTH_VENCRYPT_X509SASL = 263,
VNC_AUTH_VENCRYPT_TLSSASL = 264,
};
......@@ -256,6 +265,8 @@ enum {
void vnc_client_read(void *opaque);
void vnc_client_write(void *opaque);
long vnc_client_read_buf(VncState *vs, uint8_t *data, size_t datalen);
long vnc_client_write_buf(VncState *vs, const uint8_t *data, size_t datalen);
/* Protocol I/O functions */
void vnc_write(VncState *vs, const void *data, size_t len);
......@@ -275,8 +286,22 @@ uint32_t read_u32(uint8_t *data, size_t offset);
/* Protocol stage functions */
void vnc_client_error(VncState *vs);
int vnc_client_io_error(VncState *vs, int ret, int last_errno);
void start_client_init(VncState *vs);
void start_auth_vnc(VncState *vs);
/* Buffer management */
void buffer_reserve(Buffer *buffer, size_t len);
int buffer_empty(Buffer *buffer);
uint8_t *buffer_end(Buffer *buffer);
void buffer_reset(Buffer *buffer);
void buffer_append(Buffer *buffer, const void *data, size_t len);
/* Misc helpers */
char *vnc_socket_local_addr(const char *format, int fd);
char *vnc_socket_remote_addr(const char *format, int fd);
#endif /* __QEMU_VNC_H */
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