vnc: allow specifying a custom authorization object name

The VNC server has historically had support for ACLs to check both the
SASL username and the TLS x509 distinguished name. The VNC server was
responsible for creating the initial ACL, and the client app was then
responsible for populating it with rules using the HMP 'acl_add' command.

This is not satisfactory for a variety of reasons. There is no way to
populate the ACLs from the command line, users are forced to use the
HMP. With multiple network services all supporting TLS and ACLs now, it
is desirable to be able to define a single ACL that is referenced by all
services.

To address these limitations, two new options are added to the VNC
server CLI. The 'tls-authz' option takes the ID of a QAuthZ object to
use for checking TLS x509 distinguished names, and the 'sasl-authz'
option takes the ID of another object to use for checking SASL usernames.

In this example, we setup two authorization rules. The first allows any
client with a certificate issued by the 'RedHat' organization in the
'London' locality. The second ACL allows clients with either the
'joe@REDHAT.COM' or  'fred@REDHAT.COM' kerberos usernames. Both checks
must pass for the user to be allowed.

    $QEMU -object tls-creds-x509,id=tls0,dir=/home/berrange/qemutls,\
                  endpoint=server,verify-peer=yes \
          -object authz-simple,id=authz0,policy=deny,\
                  rules.0.match=O=RedHat,,L=London,rules.0.policy=allow \
          -object authz-simple,id=authz1,policy=deny,\
                  rules.0.match=fred@REDHAT.COM,rules.0.policy=allow \
                  rules.0.match=joe@REDHAT.COM,rules.0.policy=allow \
          -vnc 0.0.0.0:1,tls-creds=tls0,tls-authz=authz0,
	       sasl,sasl-authz=authz1 \
          ...other QEMU args...

Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20190227145755.26556-2-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Daniel P. Berrange 2019-02-27 14:57:54 +00:00 committed by Gerd Hoffmann
parent bbcdeb623d
commit 55cf09a02b
3 changed files with 79 additions and 19 deletions

View File

@ -60,6 +60,11 @@ Support for invalid topologies will be removed, the user must ensure
topologies described with -smp include all possible cpus, i.e. topologies described with -smp include all possible cpus, i.e.
@math{@var{sockets} * @var{cores} * @var{threads} = @var{maxcpus}}. @math{@var{sockets} * @var{cores} * @var{threads} = @var{maxcpus}}.
@subsection -vnc acl (since 4.0.0)
The @code{acl} option to the @code{-vnc} argument has been replaced
by the @code{tls-authz} and @code{sasl-authz} options.
@section QEMU Machine Protocol (QMP) commands @section QEMU Machine Protocol (QMP) commands
@subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0) @subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0)

View File

@ -1624,6 +1624,14 @@ will cause the VNC server socket to enable the VeNCrypt auth
mechanism. The credentials should have been previously created mechanism. The credentials should have been previously created
using the @option{-object tls-creds} argument. using the @option{-object tls-creds} argument.
@item tls-authz=@var{ID}
Provides the ID of the QAuthZ authorization object against which
the client's x509 distinguished name will validated. This object is
only resolved at time of use, so can be deleted and recreated on the
fly while the VNC server is active. If missing, it will default
to denying access.
@item sasl @item sasl
Require that the client use SASL to authenticate with the VNC server. Require that the client use SASL to authenticate with the VNC server.
@ -1639,18 +1647,25 @@ ensures a data encryption preventing compromise of authentication
credentials. See the @ref{vnc_security} section for details on using credentials. See the @ref{vnc_security} section for details on using
SASL authentication. SASL authentication.
@item sasl-authz=@var{ID}
Provides the ID of the QAuthZ authorization object against which
the client's SASL username will validated. This object is
only resolved at time of use, so can be deleted and recreated on the
fly while the VNC server is active. If missing, it will default
to denying access.
@item acl @item acl
Turn on access control lists for checking of the x509 client certificate Legacy method for enabling authorization of clients against the
and SASL party. For x509 certs, the ACL check is made against the x509 distinguished name and SASL username. It results in the creation
certificate's distinguished name. This is something that looks like of two @code{authz-list} objects with IDs of @code{vnc.username} and
@code{C=GB,O=ACME,L=Boston,CN=bob}. For SASL party, the ACL check is @code{vnc.x509dname}. The rules for these objects must be configured
made against the username, which depending on the SASL plugin, may with the HMP ACL commands.
include a realm component, eg @code{bob} or @code{bob@@EXAMPLE.COM}.
When the @option{acl} flag is set, the initial access list will be This option is deprecated and should no longer be used. The new
empty, with a @code{deny} policy. Thus no one will be allowed to @option{sasl-authz} and @option{tls-authz} options are a
use the VNC server until the ACLs have been loaded. This can be replacement.
achieved using the @code{acl} monitor command.
@item lossy @item lossy

View File

@ -3363,6 +3363,12 @@ static QemuOptsList qemu_vnc_opts = {
},{ },{
.name = "acl", .name = "acl",
.type = QEMU_OPT_BOOL, .type = QEMU_OPT_BOOL,
},{
.name = "tls-authz",
.type = QEMU_OPT_STRING,
},{
.name = "sasl-authz",
.type = QEMU_OPT_STRING,
},{ },{
.name = "lossy", .name = "lossy",
.type = QEMU_OPT_BOOL, .type = QEMU_OPT_BOOL,
@ -3802,6 +3808,8 @@ void vnc_display_open(const char *id, Error **errp)
const char *credid; const char *credid;
bool sasl = false; bool sasl = false;
int acl = 0; int acl = 0;
const char *tlsauthz;
const char *saslauthz;
int lock_key_sync = 1; int lock_key_sync = 1;
int key_delay_ms; int key_delay_ms;
@ -3873,7 +3881,33 @@ void vnc_display_open(const char *id, Error **errp)
goto fail; goto fail;
} }
} }
if (qemu_opt_get(opts, "acl")) {
error_report("The 'acl' option to -vnc is deprecated. "
"Please use the 'tls-authz' and 'sasl-authz' "
"options instead");
}
acl = qemu_opt_get_bool(opts, "acl", false); acl = qemu_opt_get_bool(opts, "acl", false);
tlsauthz = qemu_opt_get(opts, "tls-authz");
if (acl && tlsauthz) {
error_setg(errp, "'acl' option is mutually exclusive with the "
"'tls-authz' option");
goto fail;
}
if (tlsauthz && !vd->tlscreds) {
error_setg(errp, "'tls-authz' provided but TLS is not enabled");
goto fail;
}
saslauthz = qemu_opt_get(opts, "sasl-authz");
if (acl && saslauthz) {
error_setg(errp, "'acl' option is mutually exclusive with the "
"'sasl-authz' option");
goto fail;
}
if (saslauthz && !sasl) {
error_setg(errp, "'sasl-authz' provided but SASL auth is not enabled");
goto fail;
}
share = qemu_opt_get(opts, "share"); share = qemu_opt_get(opts, "share");
if (share) { if (share) {
@ -3903,7 +3937,9 @@ void vnc_display_open(const char *id, Error **errp)
vd->non_adaptive = true; vd->non_adaptive = true;
} }
if (acl) { if (tlsauthz) {
vd->tlsauthzid = g_strdup(tlsauthz);
} else if (acl) {
if (strcmp(vd->id, "default") == 0) { if (strcmp(vd->id, "default") == 0) {
vd->tlsauthzid = g_strdup("vnc.x509dname"); vd->tlsauthzid = g_strdup("vnc.x509dname");
} else { } else {
@ -3914,15 +3950,19 @@ void vnc_display_open(const char *id, Error **errp)
&error_abort)); &error_abort));
} }
#ifdef CONFIG_VNC_SASL #ifdef CONFIG_VNC_SASL
if (acl && sasl) { if (sasl) {
if (strcmp(vd->id, "default") == 0) { if (saslauthz) {
vd->sasl.authzid = g_strdup("vnc.username"); vd->sasl.authzid = g_strdup(saslauthz);
} else { } else if (acl) {
vd->sasl.authzid = g_strdup_printf("vnc.%s.username", vd->id); if (strcmp(vd->id, "default") == 0) {
vd->sasl.authzid = g_strdup("vnc.username");
} else {
vd->sasl.authzid = g_strdup_printf("vnc.%s.username", vd->id);
}
vd->sasl.authz = QAUTHZ(qauthz_list_new(vd->sasl.authzid,
QAUTHZ_LIST_POLICY_DENY,
&error_abort));
} }
vd->sasl.authz = QAUTHZ(qauthz_list_new(vd->sasl.authzid,
QAUTHZ_LIST_POLICY_DENY,
&error_abort));
} }
#endif #endif