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From: Ira Weiny <ira.weiny@intel.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>,
	mporter@kernel.crashing.org, alex.bou9@gmail.com,
	akpm@linux-foundation.org, gustavoars@kernel.org,
	jhubbard@nvidia.com, madhuparnabhowmik10@gmail.com,
	linux-kernel@vger.kernel.org,
	Matthew Wilcox <willy@infradead.org>
Subject: Re: [linux-next PATCH] rapidio: Fix error handling path
Date: Wed, 16 Sep 2020 08:16:09 -0700	[thread overview]
Message-ID: <20200916151607.GB2485491@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200916100232.GF18329@kadam>

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
> 

  parent reply	other threads:[~2020-09-16 20:58 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-16  3:42 [linux-next PATCH] rapidio: Fix error handling path Souptick Joarder
2020-09-16  6:37 ` John Hubbard
2020-09-16 10:02 ` Dan Carpenter
2020-09-16 10:07   ` Dan Carpenter
2020-09-16 15:16   ` Ira Weiny [this message]
2020-09-16 15:27     ` Dan Carpenter
2020-09-17  6:57   ` [PATCH] mm/gup: protect unpin_user_pages() against npages==-ERRNO John Hubbard
2020-09-17  7:40     ` Dan Carpenter
2020-09-20  3:03       ` Souptick Joarder
2020-09-20  4:13         ` John Hubbard
2020-09-21  9:34           ` Dan Carpenter
2020-09-17 12:39   ` [linux-next PATCH] rapidio: Fix error handling path Dan Carpenter
2020-09-17 17:34     ` Ira Weiny
2020-09-17 17:47       ` John Hubbard
2020-09-18  2:21         ` Souptick Joarder
2020-09-18  6:33           ` John Hubbard
2020-09-18  2:25     ` Souptick Joarder
2020-09-18  6:15       ` Dan Carpenter
2020-09-16 15:20 ` Ira Weiny

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