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

[Ira Weiny]

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.

Ira

> 
> It's not possible to pin more than "ULONG_MAX - 4095" because otherwise
> returning error pointers wouldn't work.  So this check can't break
> anything and it could prevent a crash.
> 
> regards,
> dan carpenter
>