Re: [Qemu-devel] [PATCH] qmp: object-add: Validate class before creating object

[Eduardo Habkost]

On Wed, Apr 16, 2014 at 08:53:23AM +0200, Markus Armbruster wrote:
> Eduardo Habkost <address@hidden> writes:
> 
> > Currently it is very easy to crash QEMU by issuing an object-add command
> > using an abstract class or a class that doesn't support
> > TYPE_USER_CREATABLE as parameter.
> >
> > Example: with the following QMP command:
> >
> >     (QEMU) object-add qom-type=cpu id=foo
> >
> > QEMU aborts at:
> >
> >     ERROR:qom/object.c:335:object_initialize_with_type: assertion failed: 
> > (type->abstract == false)
> >
> > This patch moves the check for TYPE_USER_CREATABLE before object_new(),
> > and adds a check to prevent the code from trying to instantiate abstract
> > classes.
> >
> > Signed-off-by: Eduardo Habkost <address@hidden>
> 
> Related device_add fixes:
> 
> 061e84f qdev-monitor: Avoid device_add crashing on non-device driver name
> 2fa4e56 qdev-monitor: Fix crash when device_add is called with abstract driver
> 7ea5e78 qdev: Do not let the user try to device_add when it cannot work
> 
> > ---
> >  qmp.c | 21 ++++++++++++++-------
> >  1 file changed, 14 insertions(+), 7 deletions(-)
> >
> > diff --git a/qmp.c b/qmp.c
> > index 87a28f7..e7ecbb7 100644
> > --- a/qmp.c
> > +++ b/qmp.c
> > @@ -540,14 +540,27 @@ void object_add(const char *type, const char *id, 
> > const QDict *qdict,
> >                  Visitor *v, Error **errp)
> >  {
> >      Object *obj;
> > +    ObjectClass *klass;
> >      const QDictEntry *e;
> >      Error *local_err = NULL;
> >  
> > -    if (!object_class_by_name(type)) {
> > +    klass = object_class_by_name(type);
> > +    if (!klass) {
> >          error_setg(errp, "invalid class name");
> >          return;
> >      }
> >  
> > +    if (object_class_is_abstract(klass)) {
> > +        error_setg(errp, "object type '%s' is abstract", type);
> > +        return;
> > +    }
> > +
> > +    if (!object_class_dynamic_cast(klass, TYPE_USER_CREATABLE)) {
> > +        error_setg(errp, "object type '%s' isn't supported by object-add",
> > +                   type);
> > +        return;
> > +    }
> > +
> >      obj = object_new(type);
> >      if (qdict) {
> >          for (e = qdict_first(qdict); e; e = qdict_next(qdict, e)) {
> 
> For comparison, this is qdev_device_add():
> 
>     oc = object_class_by_name(driver);
>     if (!oc) {
>         const char *typename = find_typename_by_alias(driver);
> 
>         if (typename) {
>             driver = typename;
>             oc = object_class_by_name(driver);
>         }
>     }
> 
>     if (!object_class_dynamic_cast(oc, TYPE_DEVICE)) {
>         qerror_report(ERROR_CLASS_GENERIC_ERROR,
>                       "'%s' is not a valid device model name", driver);
>         return NULL;
>     }
> 
>     if (object_class_is_abstract(oc)) {
>         qerror_report(QERR_INVALID_PARAMETER_VALUE, "driver",
>                       "non-abstract device type");
>         return NULL;
>     }
> 
>     dc = DEVICE_CLASS(oc);
>     if (dc->cannot_instantiate_with_device_add_yet) {
>         qerror_report(QERR_INVALID_PARAMETER_VALUE, "driver",
>                       "pluggable device type");
>         return NULL;
>     }
> 
> Got the "subtype of" and the "not abstract" check in the opposite order,
> and the additional cannot_instantiate_with_device_add_yet check.
> 
> Does the different order matter?

The order probably doesn't matter very much. But it makes sense to keep
it similar to device_add for consistency. I will send v2.


> > @@ -558,12 +571,6 @@ void object_add(const char *type, const char *id, 
> > const QDict *qdict,
> >          }
> >      }
> >  
> > -    if (!object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > -        error_setg(&local_err, "object type '%s' isn't supported by 
> > object-add",
> > -                   type);
> > -        goto out;
> > -    }
> > -
> >      user_creatable_complete(obj, &local_err);
> >      if (local_err) {
> >          goto out;

-- 
Eduardo