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

Dan Carpenter
2020-09-16T10:08:49Z

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;
>
> 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.

Actually pin_user_pages_fast() returns an int. It's not possible to
pin more than INT_MAX.

regards,
dan carpenter