Re: [Qemu-devel] [PATCH v3 10/10] vnc: allow specifying a custom ACL object name

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

On Tue, Mar 22, 2016 at 03:38:14PM -0600, Eric Blake wrote:
> On 03/10/2016 11:59 AM, Daniel P. Berrange wrote:
> > 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-acl' option takes the ID of a QAuthZ
> > object to use for checking TLS x509 distinguished names, and
> > the 'sasl-acl' option takes the ID of another object to use for
> > checking SASL usernames.
> > 
> > In this example, we setup two ACLs. 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 ACLs 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=acl0,policy=deny,\
> >                   rules.0.match=O=RedHat,,L=London,rules.0.policy=allow \
> >           -object authz-simple,id=acl0,policy=deny,\
> 
> Umm, you can't reuse 'acl0' as the id.
> 
> >                   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-acl=tlsacl0,
> > 	       sasl,sasl-acl=saslacl0 \
> 
> And this fails because the ids don't exist.  I think you meant
> authz-simple,id=tlsacl0 in the first instance, and
> authz-simple,id=saslacl0 in the second instance.

Heh, yeah, I really ought to try the examples I put in the commit
message tomake sure they work :-)

> > Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> > ---
> >  ui/vnc.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++------------
> >  1 file changed, 60 insertions(+), 13 deletions(-)
> > 
> > @@ -3670,6 +3680,21 @@ void vnc_display_open(const char *id, Error **errp)
> >          }
> >      }
> >      acl = qemu_opt_get_bool(opts, "acl", false);
> > +    tlsacl = qemu_opt_get(opts, "tls-acl");
> > +    if (acl && tlsacl) {
> > +        error_setg(errp, "'acl' option is mutually exclusive with the "
> > +                   "'tls-acl' options");
> > +        goto fail;
> > +    }
> > +
> > +#ifdef CONFIG_VNC_SASL
> > +    saslacl = qemu_opt_get(opts, "sasl-acl");
> > +    if (acl && saslacl) {
> > +        error_setg(errp, "'acl' option is mutually exclusive with the "
> > +                   "'sasl-acl' options");
> > +        goto fail;
> > +    }
> > +#endif
> 
> Do we explicitly fail if sasl-acl was provided but CONFIG_VNC_SASL is
> not defined?  It looks here like you silently ignore it, which would not
> be good.

Yes, we should really raise the error unconditionally.

> > @@ -3710,19 +3737,39 @@ void vnc_display_open(const char *id, Error **errp)
> >                            &error_abort);
> >      }
> >  #ifdef CONFIG_VNC_SASL
> > -    if (acl && sasl) {
> > -        char *aclname;
> > +    if (sasl) {
> > +        if (saslacl) {
> > +            Object *container, *acl;
> > +            container = object_get_objects_root();
> > +            acl = object_resolve_path_component(container, saslacl);
> > +            if (!acl) {
> > +                error_setg(errp, "Cannot find ACL %s", saslacl);
> > +                goto fail;
> > +            }
> >  
> > -        if (strcmp(vs->id, "default") == 0) {
> > -            aclname = g_strdup("vnc.username");
> > -        } else {
> > -            aclname = g_strdup_printf("vnc.%s.username", vs->id);
> > -        }
> > -        vs->sasl.acl =
> > -            QAUTHZ(qauthz_simple_new(aclname,
> > -                                     QAUTHZ_SIMPLE_POLICY_DENY,
> > -                                     &error_abort));
> > -        g_free(aclname);
> > +            if (!object_dynamic_cast(acl, TYPE_QAUTHZ)) {
> > +                error_setg(errp, "Object '%s' is not a QAuthZ subclass",
> > +                           saslacl);
> > +                goto fail;
> > +            }
> > +            vs->sasl.acl = QAUTHZ(acl);
> > +        } else if (acl) {
> > +            char *aclname;
> > +
> > +            if (strcmp(vs->id, "default") == 0) {
> > +                aclname = g_strdup("vnc.username");
> > +            } else {
> > +                aclname = g_strdup_printf("vnc.%s.username", vs->id);
> > +            }
> > +            vs->sasl.acl =
> > +                QAUTHZ(qauthz_simple_new(aclname,
> > +                                         QAUTHZ_SIMPLE_POLICY_DENY,
> > +                                         &error_abort));
> > +            g_free(aclname);
> > +        }
> > +    } else if (saslacl) {
> > +        error_setg(errp, "SASL ACL provided when SASL is disabled");
> > +        goto fail;
> >      }
> >  #endif
> >  
> 
> Again, the saslacl check is only mentioned inside the #if; what happens
> when the #if is not compiled?

Yeah, I should fix that.


Regards,
Daniel
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