Re: [linux-next PATCH] rapidio: Fix error handling path

Dan Carpenter
2020-09-16T20:34:40Z

On Wed, Sep 16, 2020 at 08:16:09AM -0700, Ira Weiny wrote:
> On Wed, Sep 16, 2020 at 01:02:32PM +0300, Dan Carpenter wrote:
> > On Wed, Sep 16, 2020 at 09:12:17AM +0530, Souptick Joarder wrote:
> > > There is an error when pin_user_pages_fast() returns -ERRNO and
> > > inside error handling path driver end up calling unpin_user_pages()
> > > with -ERRNO which is not correct.
> > >
> > > This patch will fix the problem.
> >
> > There are a few ways we could prevent bug in the future.
> >
> > 1) This could have been caught with existing static analysis tools
> > which warn about when a value is set but not used.
> >
> > 2) I've created a Smatch check which warngs about:
> >
> > drivers/rapidio/devices/rio_mport_cdev.c:955 rio_dma_transfer() warn: unpinning negative pages 'nr_pages'
> >
> > I'll test it out tonight and see how well it works. I don't
> > immediately see any other bugs allthough Smatch doesn't like the code
> > in siw_umem_release(). It uses "min_t(int" which suggests that
> > negative pages are okay.
> >
> > int to_free = min_t(int, PAGES_PER_CHUNK, num_pages);
> >
> > 3) We could add a check in unpin_user_pages().
> >
> > if (WARN_ON(IS_ERR_VALUE(npages)))
> > return;
>
> Does IS_ERR_VALUE() work on an unsigned variable? The issue with adding a
> check in unpin_user_pages() is that npages is unsigned long.

Yeah, it does. It only works on long and unsigned long.

(Or long long types if they have the same number of bytes as a long).

regards,
dan carpenter