Re: [PATCH 2/2] staging: emxx_udc: test returned value

[Julia Lawall <julia.lawall@lip6.fr>]

On Sat, 4 Apr 2015, Greg Kroah-Hartman wrote:

> On Sat, Apr 04, 2015 at 04:59:30PM +0200, Julia Lawall wrote:
> > Put NULL test on the result of the previous call instead on one of its
> > arguments.  A simplified version of the semantic match that finds this
> > problem is as follows (http://coccinelle.lip6.fr/):
> > 
> > // <smpl>
> > r@
> > expression *e1;
> > expression *e2;
> > identifier f;
> > statement S1,S2;
> > @@
> > 
> > e1 = f(...,e2,...);
> > (
> > if (e1 == NULL || ...) S1 else S2
> > |
> > *if (e2 == NULL || ...) S1 else S2
> > )
> > // </smpl>
> > 
> > Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> > 
> > ---
> >  drivers/staging/emxx_udc/emxx_udc.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/staging/emxx_udc/emxx_udc.c b/drivers/staging/emxx_udc/emxx_udc.c
> > index fbf82bc..7de1e9e 100644
> > --- a/drivers/staging/emxx_udc/emxx_udc.c
> > +++ b/drivers/staging/emxx_udc/emxx_udc.c
> > @@ -2998,7 +2998,7 @@ static void  nbu2ss_ep_fifo_flush(struct usb_ep *_ep)
> >  	}
> >  
> >  	ep = container_of(_ep, struct nbu2ss_ep, ep);
> > -	if (!_ep) {
> > +	if (!ep) {
> 
> This is actually even worse, container_of() can't return NULL.  Or if it
> does, something is really wrong (it can only happen if the field happens
> to be the first field in the structure and the original pointer was
> NULL).  So I would say that all tests for container_of (and
> functions/macros that are just wrappers around container_of()) can just
> be deleted as they will never be triggered.

Couldn't one say:

x = NULL;
y = &x->whatever;
z = container_of(y, struct blah, whatever);

and end up with z being NULL?

> Not to say that this patch is wrong at all, I'll go apply it, and you
> should add it to the lists of tests in the kernel source, but you should
> also consider making a test to catch container_of() results.
> 
> Hm, now that I know coccinelle, I guess I should be able to do this :)

Yes indeed :)

julia