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

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Message-ID: <1ec3dab9-9716-4413-5a3b-9a492259712d@nvidia.com>
Date:   Tue, 15 Sep 2020 23:37:52 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Souptick Joarder <jrdr.linux@...il.com>,
        <mporter@...nel.crashing.org>, <alex.bou9@...il.com>,
        <akpm@...ux-foundation.org>, <gustavoars@...nel.org>,
        <madhuparnabhowmik10@...il.com>, <dan.carpenter@...cle.com>
CC:     <linux-kernel@...r.kernel.org>, Ira Weiny <ira.weiny@...el.com>,
        "Matthew Wilcox" <willy@...radead.org>
Subject: Re: [linux-next PATCH] rapidio: Fix error handling path

On 9/15/20 8:42 PM, 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.

How about:

rio_dma_transfer() attempts to clamp the return value of
pin_user_pages_fast() to be >= 0. However, the attempt fails because
nr_pages is overridden a few lines later, and restored to the
undesirable -ERRNO value.

The return value is ultimately stored in nr_pages, which in turn is
passed to unpin_user_pages(), which expects nr_pages >= 0, else,
disaster.

Fix this by fixing the nesting of the assignment to nr_pages: nr_pages
should be clamped to zero if pin_user_pages_fast() returns -ERRNO, or
set to the return value of pin_user_pages_fast(), otherwise.

> 
> Fixes: e8de370188d09 ("rapidio: add mport char device driver")
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> ---
>   drivers/rapidio/devices/rio_mport_cdev.c | 13 +++++++------
>   1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
> index a303429..163b6c72 100644
> --- a/drivers/rapidio/devices/rio_mport_cdev.c
> +++ b/drivers/rapidio/devices/rio_mport_cdev.c
> @@ -871,15 +871,16 @@ static int do_dma_request(struct mport_dma_req *req,
>   				rmcd_error("pin_user_pages_fast err=%ld",
>   					   pinned);
>   				nr_pages = 0;
> -			} else
> +			} else {
>   				rmcd_error("pinned %ld out of %ld pages",
>   					   pinned, nr_pages);
> +				/*
> +				 * Set nr_pages up to mean "how many pages to unpin, in
> +				 * the error handler:
> +				 */
> +				nr_pages = pinned;
> +			}
>   			ret = -EFAULT;
> -			/*
> -			 * Set nr_pages up to mean "how many pages to unpin, in
> -			 * the error handler:
> -			 */
> -			nr_pages = pinned;
>   			goto err_pg;
>   		}
>   
> 

Reviewed-by: John Hubbard <jhubbard@...dia.com>

thanks,
-- 
John Hubbard
NVIDIA