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

[Dan Carpenter]

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