Re: [Qemu-devel] [PATCH 1/4] qjson: Improve debugging

[Luiz Capitulino]

On Thu, 04 Feb 2010 16:31:46 -0600
Anthony Liguori <address@hidden> wrote:

> On 02/04/2010 02:13 PM, Luiz Capitulino wrote:
> > Add an assert() to qobject_from_jsonf() to assure that the returned
> > QObject is not NULL. Currently this is duplicated in the callers.
> >
> > Signed-off-by: Luiz Capitulino<address@hidden>
> > ---
> >   qjson.c |    1 +
> >   1 files changed, 1 insertions(+), 0 deletions(-)
> >
> > diff --git a/qjson.c b/qjson.c
> > index 9ad8a91..0922c06 100644
> > --- a/qjson.c
> > +++ b/qjson.c
> > @@ -62,6 +62,7 @@ QObject *qobject_from_jsonf(const char *string, ...)
> >       obj = qobject_from_jsonv(string,&ap);
> >       va_end(ap);
> >
> > +    assert(obj != NULL);
> >    
> 
> This is wrong.  We may get JSON from an untrusted source.  Callers need 
> to deal with failure appropriately.

 What kind of untrusted source? This function is only used by handlers
and assuming that the only possible error here is bad syntax, not having
this check in the source will only duplicate it in the users.

> It just so happens that we only parse JSON from an untrusted source via 
> qobject_from_json(), but the trust relationship is not obvious given the 
> two functions in their current form.

 Not exactly, qobject_from_json() is not even being currently used.

 We parse JSON data from clients by using the low-level parser API,
that's by calling json_message_parser_feed() to read the input and
then calling json_parser_parse() when we have collected enough data.

 qobject_from_jsonf() is only used internally, by handlers.

 Both, qobject_from_jsonf() and qobject_from_json() are _wrappers_ to
qobject_from_jsonv(), which uses the low-level API directly.

 So, having the assert() in qobject_from_jsonf() should only
affect handlers, which seems fine to me.