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authz: add QAuthZPAM object type for authorizing using PAM

Add an authorization backend that talks to PAM to check whether the user
identity is allowed. This only uses the PAM account validation facility,
which is essentially just a check to see if the provided username is permitted
access. It doesn't use the authentication or session parts of PAM, since
that's dealt with by the relevant part of QEMU (eg VNC server).

Consider starting QEMU with a VNC server and telling it to use TLS with
x509 client certificates and configuring it to use an PAM to validate
the x509 distinguished name. In this example we're telling it to use PAM
for the QAuthZ impl with a service name of "qemu-vnc"

 $ qemu-system-x86_64 \
     -object tls-creds-x509,id=tls0,dir=/home/berrange/security/qemutls,\
             endpoint=server,verify-peer=yes \
     -object authz-pam,id=authz0,service=qemu-vnc \
     -vnc :1,tls-creds=tls0,tls-authz=authz0

This requires an /etc/pam/qemu-vnc file to be created with the auth
rules. A very simple file based whitelist can be setup using

  $ cat > /etc/pam/qemu-vnc <<EOF
  account         requisite       pam_listfile.so item=user sense=allow file=/etc/qemu/vnc.allow
  EOF

The /etc/qemu/vnc.allow file simply contains one username per line. Any
username not in the file is denied. The usernames in this example are
the x509 distinguished name from the client's x509 cert.

  $ cat > /etc/qemu/vnc.allow <<EOF
  CN=laptop.berrange.com,O=Berrange Home,L=London,ST=London,C=GB
  EOF

More interesting would be to configure PAM to use an LDAP backend, so
that the QEMU authorization check data can be centralized instead of
requiring each compute host to have file maintained.

The main limitation with this PAM module is that the rules apply to all
QEMU instances on the host. Setting up different rules per VM, would
require creating a separate PAM service name & config file for every
guest. An alternative approach for the future might be to not pass in
the plain username to PAM, but instead combine the VM name or UUID with
the username. This requires further consideration though.

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
tags/v4.0.0-rc0
Daniel P. Berrange 3 years ago
parent
commit
8953caf3cd
8 changed files with 452 additions and 0 deletions
  1. +3
    -0
      authz/Makefile.objs
  2. +148
    -0
      authz/pamacct.c
  3. +3
    -0
      authz/trace-events
  4. +37
    -0
      configure
  5. +100
    -0
      include/authz/pamacct.h
  6. +35
    -0
      qemu-options.hx
  7. +2
    -0
      tests/Makefile.include
  8. +124
    -0
      tests/test-authz-pam.c

+ 3
- 0
authz/Makefile.objs View File

@@ -2,3 +2,6 @@ authz-obj-y += base.o
authz-obj-y += simple.o
authz-obj-y += list.o
authz-obj-y += listfile.o
authz-obj-$(CONFIG_AUTH_PAM) += pamacct.o

pamacct.o-libs = -lpam

+ 148
- 0
authz/pamacct.c View File

@@ -0,0 +1,148 @@
/*
* QEMU PAM authorization driver
*
* Copyright (c) 2018 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/

#include "qemu/osdep.h"
#include "authz/pamacct.h"
#include "authz/trace.h"
#include "qom/object_interfaces.h"

#include <security/pam_appl.h>


static bool qauthz_pam_is_allowed(QAuthZ *authz,
const char *identity,
Error **errp)
{
QAuthZPAM *pauthz = QAUTHZ_PAM(authz);
const struct pam_conv pam_conversation = { 0 };
pam_handle_t *pamh = NULL;
int ret;

trace_qauthz_pam_check(authz, identity, pauthz->service);
ret = pam_start(pauthz->service,
identity,
&pam_conversation,
&pamh);
if (ret != PAM_SUCCESS) {
error_setg(errp, "Unable to start PAM transaction: %s",
pam_strerror(NULL, ret));
return false;
}

ret = pam_acct_mgmt(pamh, PAM_SILENT);
pam_end(pamh, ret);
if (ret != PAM_SUCCESS) {
error_setg(errp, "Unable to authorize user '%s': %s",
identity, pam_strerror(pamh, ret));
return false;
}

return true;
}


static void
qauthz_pam_prop_set_service(Object *obj,
const char *service,
Error **errp G_GNUC_UNUSED)
{
QAuthZPAM *pauthz = QAUTHZ_PAM(obj);

g_free(pauthz->service);
pauthz->service = g_strdup(service);
}


static char *
qauthz_pam_prop_get_service(Object *obj,
Error **errp G_GNUC_UNUSED)
{
QAuthZPAM *pauthz = QAUTHZ_PAM(obj);

return g_strdup(pauthz->service);
}


static void
qauthz_pam_complete(UserCreatable *uc, Error **errp)
{
}


static void
qauthz_pam_finalize(Object *obj)
{
QAuthZPAM *pauthz = QAUTHZ_PAM(obj);

g_free(pauthz->service);
}


static void
qauthz_pam_class_init(ObjectClass *oc, void *data)
{
UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
QAuthZClass *authz = QAUTHZ_CLASS(oc);

ucc->complete = qauthz_pam_complete;
authz->is_allowed = qauthz_pam_is_allowed;

object_class_property_add_str(oc, "service",
qauthz_pam_prop_get_service,
qauthz_pam_prop_set_service,
NULL);
}


QAuthZPAM *qauthz_pam_new(const char *id,
const char *service,
Error **errp)
{
return QAUTHZ_PAM(
object_new_with_props(TYPE_QAUTHZ_PAM,
object_get_objects_root(),
id, errp,
"service", service,
NULL));
}


static const TypeInfo qauthz_pam_info = {
.parent = TYPE_QAUTHZ,
.name = TYPE_QAUTHZ_PAM,
.instance_size = sizeof(QAuthZPAM),
.instance_finalize = qauthz_pam_finalize,
.class_size = sizeof(QAuthZPAMClass),
.class_init = qauthz_pam_class_init,
.interfaces = (InterfaceInfo[]) {
{ TYPE_USER_CREATABLE },
{ }
}
};


static void
qauthz_pam_register_types(void)
{
type_register_static(&qauthz_pam_info);
}


type_init(qauthz_pam_register_types);

+ 3
- 0
authz/trace-events View File

@@ -13,3 +13,6 @@ qauthz_list_default_policy(void *authz, const char *identity, int policy) "AuthZ
# auth/listfile.c
qauthz_list_file_load(void *authz, const char *filename) "AuthZ file %p load filename=%s"
qauthz_list_file_refresh(void *authz, const char *filename, int success) "AuthZ file %p load filename=%s success=%d"

# auth/pam.c
qauthz_pam_check(void *authz, const char *identity, const char *service) "AuthZ PAM %p identity=%s service=%s"

+ 37
- 0
configure View File

@@ -463,6 +463,7 @@ gnutls=""
nettle=""
gcrypt=""
gcrypt_hmac="no"
auth_pam=""
vte=""
virglrenderer=""
tpm="yes"
@@ -1381,6 +1382,10 @@ for opt do
;;
--enable-gcrypt) gcrypt="yes"
;;
--disable-auth-pam) auth_pam="no"
;;
--enable-auth-pam) auth_pam="yes"
;;
--enable-rdma) rdma="yes"
;;
--disable-rdma) rdma="no"
@@ -1707,6 +1712,7 @@ disabled with --disable-FEATURE, default is enabled if available:
gnutls GNUTLS cryptography support
nettle nettle cryptography support
gcrypt libgcrypt cryptography support
auth-pam PAM access control
sdl SDL UI
sdl_image SDL Image support for icons
gtk gtk UI
@@ -2864,6 +2870,33 @@ else
fi


##########################################
# PAM probe

if test "$auth_pam" != "no"; then
cat > $TMPC <<EOF
#include <security/pam_appl.h>
#include <stdio.h>
int main(void) {
const char *service_name = "qemu";
const char *user = "frank";
const struct pam_conv *pam_conv = NULL;
pam_handle_t *pamh = NULL;
pam_start(service_name, user, pam_conv, &pamh);
return 0;
}
EOF
if compile_prog "" "-lpam" ; then
auth_pam=yes
else
if test "$auth_pam" = "yes"; then
feature_not_found "PAM" "Install PAM development package"
else
auth_pam=no
fi
fi
fi

##########################################
# getifaddrs (for tests/test-io-channel-socket )

@@ -6091,6 +6124,7 @@ echo "GNUTLS support $gnutls"
echo "libgcrypt $gcrypt"
echo "nettle $nettle $(echo_version $nettle $nettle_version)"
echo "libtasn1 $tasn1"
echo "PAM $auth_pam"
echo "curses support $curses"
echo "virgl support $virglrenderer $(echo_version $virglrenderer $virgl_version)"
echo "curl support $curl"
@@ -6550,6 +6584,9 @@ fi
if test "$tasn1" = "yes" ; then
echo "CONFIG_TASN1=y" >> $config_host_mak
fi
if test "$auth_pam" = "yes" ; then
echo "CONFIG_AUTH_PAM=y" >> $config_host_mak
fi
if test "$have_ifaddrs_h" = "yes" ; then
echo "HAVE_IFADDRS_H=y" >> $config_host_mak
fi

+ 100
- 0
include/authz/pamacct.h View File

@@ -0,0 +1,100 @@
/*
* QEMU PAM authorization driver
*
* Copyright (c) 2018 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/

#ifndef QAUTHZ_PAM_H__
#define QAUTHZ_PAM_H__

#include "authz/base.h"


#define TYPE_QAUTHZ_PAM "authz-pam"

#define QAUTHZ_PAM_CLASS(klass) \
OBJECT_CLASS_CHECK(QAuthZPAMClass, (klass), \
TYPE_QAUTHZ_PAM)
#define QAUTHZ_PAM_GET_CLASS(obj) \
OBJECT_GET_CLASS(QAuthZPAMClass, (obj), \
TYPE_QAUTHZ_PAM)
#define QAUTHZ_PAM(obj) \
INTERFACE_CHECK(QAuthZPAM, (obj), \
TYPE_QAUTHZ_PAM)

typedef struct QAuthZPAM QAuthZPAM;
typedef struct QAuthZPAMClass QAuthZPAMClass;


/**
* QAuthZPAM:
*
* This authorization driver provides a PAM mechanism
* for granting access by matching user names against a
* list of globs. Each match rule has an associated policy
* and a catch all policy applies if no rule matches
*
* To create an instance of this class via QMP:
*
* {
* "execute": "object-add",
* "arguments": {
* "qom-type": "authz-pam",
* "id": "authz0",
* "parameters": {
* "service": "qemu-vnc-tls"
* }
* }
* }
*
* The driver only uses the PAM "account" verification
* subsystem. The above config would require a config
* file /etc/pam.d/qemu-vnc-tls. For a simple file
* lookup it would contain
*
* account requisite pam_listfile.so item=user sense=allow \
* file=/etc/qemu/vnc.allow
*
* The external file would then contain a list of usernames.
* If x509 cert was being used as the username, a suitable
* entry would match the distinguish name:
*
* CN=laptop.berrange.com,O=Berrange Home,L=London,ST=London,C=GB
*
* On the command line it can be created using
*
* -object authz-pam,id=authz0,service=qemu-vnc-tls
*
*/
struct QAuthZPAM {
QAuthZ parent_obj;

char *service;
};


struct QAuthZPAMClass {
QAuthZClass parent_class;
};


QAuthZPAM *qauthz_pam_new(const char *id,
const char *service,
Error **errp);


#endif /* QAUTHZ_PAM_H__ */

+ 35
- 0
qemu-options.hx View File

@@ -4435,6 +4435,41 @@ would look like:
...
@end example

@item -object authz-pam,id=@var{id},service=@var{string}

Create an authorization object that will control access to network services.

The @option{service} parameter provides the name of a PAM service to use
for authorization. It requires that a file @code{/etc/pam.d/@var{service}}
exist to provide the configuration for the @code{account} subsystem.

An example authorization object to validate a TLS x509 distinguished
name would look like:

@example
# $QEMU \
...
-object authz-pam,id=auth0,service=qemu-vnc
...
@end example

There would then be a corresponding config file for PAM at
@code{/etc/pam.d/qemu-vnc} that contains:

@example
account requisite pam_listfile.so item=user sense=allow \
file=/etc/qemu/vnc.allow
@end example

Finally the @code{/etc/qemu/vnc.allow} file would contain
the list of x509 distingished names that are permitted
access

@example
CN=laptop.example.com,O=Example Home,L=London,ST=London,C=GB
@end example


@end table

ETEXI

+ 2
- 0
tests/Makefile.include View File

@@ -119,6 +119,7 @@ check-unit-y += tests/test-util-sockets$(EXESUF)
check-unit-y += tests/test-authz-simple$(EXESUF)
check-unit-y += tests/test-authz-list$(EXESUF)
check-unit-y += tests/test-authz-listfile$(EXESUF)
check-unit-$(CONFIG_AUTH_PAM) += tests/test-authz-pam$(EXESUF)
check-unit-y += tests/test-io-task$(EXESUF)
check-unit-y += tests/test-io-channel-socket$(EXESUF)
check-unit-y += tests/test-io-channel-file$(EXESUF)
@@ -669,6 +670,7 @@ tests/test-util-sockets$(EXESUF): tests/test-util-sockets.o \
tests/test-authz-simple$(EXESUF): tests/test-authz-simple.o $(test-authz-obj-y)
tests/test-authz-list$(EXESUF): tests/test-authz-list.o $(test-authz-obj-y)
tests/test-authz-listfile$(EXESUF): tests/test-authz-listfile.o $(test-authz-obj-y)
tests/test-authz-pam$(EXESUF): tests/test-authz-pam.o $(test-authz-obj-y)
tests/test-io-task$(EXESUF): tests/test-io-task.o $(test-io-obj-y)
tests/test-io-channel-socket$(EXESUF): tests/test-io-channel-socket.o \
tests/io-channel-helpers.o tests/socket-helpers.o $(test-io-obj-y)

+ 124
- 0
tests/test-authz-pam.c View File

@@ -0,0 +1,124 @@
/*
* QEMU PAM authorization object tests
*
* Copyright (c) 2018 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/

#include "qemu/osdep.h"
#include "qapi/error.h"
#include "authz/pamacct.h"

#include <security/pam_appl.h>

static bool failauth;

/*
* These two functions are exported by libpam.so.
*
* By defining them again here, our impls are resolved
* by the linker instead of those in libpam.so
*
* The test suite is thus isolated from the host system
* PAM setup, so we can do predictable test scenarios
*/
int
pam_start(const char *service_name, const char *user,
const struct pam_conv *pam_conversation,
pam_handle_t **pamh)
{
failauth = true;
if (!g_str_equal(service_name, "qemu-vnc")) {
return PAM_AUTH_ERR;
}

if (g_str_equal(user, "fred")) {
failauth = false;
}

return PAM_SUCCESS;
}


int
pam_acct_mgmt(pam_handle_t *pamh, int flags)
{
if (failauth) {
return PAM_AUTH_ERR;
}

return PAM_SUCCESS;
}


static void test_authz_unknown_service(void)
{
Error *local_err = NULL;
QAuthZPAM *auth = qauthz_pam_new("auth0",
"qemu-does-not-exist",
&error_abort);

g_assert_nonnull(auth);

g_assert_false(qauthz_is_allowed(QAUTHZ(auth), "fred", &local_err));

error_free_or_abort(&local_err);
object_unparent(OBJECT(auth));
}


static void test_authz_good_user(void)
{
QAuthZPAM *auth = qauthz_pam_new("auth0",
"qemu-vnc",
&error_abort);

g_assert_nonnull(auth);

g_assert_true(qauthz_is_allowed(QAUTHZ(auth), "fred", &error_abort));

object_unparent(OBJECT(auth));
}


static void test_authz_bad_user(void)
{
Error *local_err = NULL;
QAuthZPAM *auth = qauthz_pam_new("auth0",
"qemu-vnc",
&error_abort);

g_assert_nonnull(auth);

g_assert_false(qauthz_is_allowed(QAUTHZ(auth), "bob", &local_err));

error_free_or_abort(&local_err);
object_unparent(OBJECT(auth));
}


int main(int argc, char **argv)
{
g_test_init(&argc, &argv, NULL);

module_call_init(MODULE_INIT_QOM);

g_test_add_func("/auth/pam/unknown-service", test_authz_unknown_service);
g_test_add_func("/auth/pam/good-user", test_authz_good_user);
g_test_add_func("/auth/pam/bad-user", test_authz_bad_user);

return g_test_run();
}

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