[Qemu-devel] [PATCH v9 10/11] util: add QAuthZPAM object type for authorizing using PAM

["Daniel P. Berrange" <berrange@redhat.com>]

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 ACL to validate the x509 distinguished name. IN this
example we're telling it to use PAM for the ACL 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=acl0,service=qemu-vnc \
     -vnc :1,tls-creds=tls0,tls-acl=acl0

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.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 configure                |  36 ++++++++++++
 include/qemu/authz-pam.h |  98 +++++++++++++++++++++++++++++++
 util/Makefile.objs       |   3 +
 util/authz-pam.c         | 148 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 285 insertions(+)
 create mode 100644 include/qemu/authz-pam.h
 create mode 100644 util/authz-pam.c

diff --git a/configure b/configure
index 8d84919..ec1d9b1 100755
--- a/configure
+++ b/configure
@@ -312,6 +312,7 @@ nettle=""
 nettle_kdf="no"
 gcrypt=""
 gcrypt_kdf="no"
+pam=""
 vte=""
 virglrenderer=""
 tpm="yes"
@@ -1112,6 +1113,10 @@ for opt do
   ;;
   --enable-gcrypt) gcrypt="yes"
   ;;
+  --disable-pam) pam="no"
+  ;;
+  --enable-pam) pam="yes"
+  ;;
   --enable-rdma) rdma="yes"
   ;;
   --disable-rdma) rdma="no"
@@ -1332,6 +1337,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   gnutls          GNUTLS cryptography support
   nettle          nettle cryptography support
   gcrypt          libgcrypt cryptography support
+  pam             PAM access control
   sdl             SDL UI
   --with-sdlabi     select preferred SDL ABI 1.2 or 2.0
   gtk             gtk UI
@@ -2396,6 +2402,32 @@ fi
 
 
 ##########################################
+# PAM probe
+
+if test "x$pam" != "no"; then
+    cat > $TMPC <<EOF
+#include <security/pam_appl.h>
+#include <stdio.h>
+int main(void) {
+   const char *service_name = "qemu";
+   const char *user = "frank";
+   const struct pam_conv *pam_conv = NULL;
+   pam_handle_t *pamh = NULL;
+   pam_start(service_name, user, pam_conv, &pamh);
+}
+EOF
+    if compile_prog "" "-lpam" ; then
+	pam=yes
+    else
+	if test "$pam" = "yes"; then
+	    feature_not_found "PAM" "Install pam-devel"
+	else
+	    pam=no
+	fi
+    fi
+fi
+
+##########################################
 # getifaddrs (for tests/test-io-channel-socket )
 
 have_ifaddrs_h=yes
@@ -4819,6 +4851,7 @@ echo "libgcrypt kdf     $gcrypt_kdf"
 echo "nettle            $nettle $(echo_version $nettle $nettle_version)"
 echo "nettle kdf        $nettle_kdf"
 echo "libtasn1          $tasn1"
+echo "PAM               $pam"
 echo "curses support    $curses"
 echo "virgl support     $virglrenderer"
 echo "curl support      $curl"
@@ -5198,6 +5231,9 @@ fi
 if test "$tasn1" = "yes" ; then
   echo "CONFIG_TASN1=y" >> $config_host_mak
 fi
+if test "$pam" = "yes" ; then
+    echo "CONFIG_PAM=y" >> $config_host_mak
+fi
 if test "$have_ifaddrs_h" = "yes" ; then
     echo "HAVE_IFADDRS_H=y" >> $config_host_mak
 fi
diff --git a/include/qemu/authz-pam.h b/include/qemu/authz-pam.h
new file mode 100644
index 0000000..dba0289
--- /dev/null
+++ b/include/qemu/authz-pam.h
@@ -0,0 +1,98 @@
+/*
+ * QEMU pam authorization driver
+ *
+ * Copyright (c) 2016 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 "qemu/authz.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": "auth0",
+ *      "parameters": {
+ *        "rules": [
+ *           { "match": "fred", "policy": "allow", "format": "exact" },
+ *           { "match": "bob", "policy": "allow", "format": "exact" },
+ *           { "match": "danb", "policy": "deny", "format": "exact" },
+ *           { "match": "dan*", "policy": "allow", "format": "glob" }
+ *        ],
+ *        "policy": "deny"
+ *      }
+ *    }
+ *  }
+ *
+ * Or via the CLI:
+ *
+ *   $QEMU                                                         \
+ *    -object authz-pam,id=acl0,policy=deny,                    \
+ *            match.0.name=fred,match.0.policy=allow,format=exact, \
+ *            match.1.name=bob,match.1.policy=allow,format=exact,  \
+ *            match.2.name=danb,match.2.policy=deny,format=exact,  \
+ *            match.3.name=dan\*,match.3.policy=allow,format=exact
+ *
+ */
+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__ */
+
diff --git a/util/Makefile.objs b/util/Makefile.objs
index 08b5f91..dfb8e42 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -36,4 +36,7 @@ util-obj-y += qht.o
 util-obj-y += range.o
 
 util-qom-obj-y += authz.o
+util-qom-obj-$(CONFIG_PAM) += authz-pam.o
 util-qom-obj-y += authz-simple.o
+
+authz-pam.o-libs = -lpam
diff --git a/util/authz-pam.c b/util/authz-pam.c
new file mode 100644
index 0000000..d38527e
--- /dev/null
+++ b/util/authz-pam.c
@@ -0,0 +1,148 @@
+/*
+ * QEMU pam authorization driver
+ *
+ * Copyright (c) 2016 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 "qemu/authz-pam.h"
+#include "qom/object_interfaces.h"
+#include "qapi-visit.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;
+
+    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);
+    if (ret != PAM_SUCCESS) {
+        error_setg(errp, "Unable to authorize user '%s': %s",
+                   identity, pam_strerror(pamh, ret));
+        goto cleanup;
+    }
+
+ cleanup:
+    pam_end(pamh, ret);
+    return ret == PAM_SUCCESS;
+}
+
+
+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);
-- 
2.7.4