From patchwork Thu Nov 22 15:20:44 2012
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Subject: Patch to solve NULL pointer dereference in physmap_of.c
From: "Prins Anton \(ST-CO/ENG1.1\)" <Anton.Prins@nl.bosch.com>
X-Patchwork-Id: 201066
Message-Id: <85D877DD6EE67B4A9FCA9B9C3A4865670C3AF1D4E4@SI-MBX14.de.bosch.com>
To: "dedekind1@gmail.com" <dedekind1@gmail.com>
Cc: "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>
Date: Thu, 22 Nov 2012 16:20:44 +0100

[PATCH] mtd: maps/physmap_of.c: change error checking to prevent a NULL pointer dereference if no DTS tuple is mappable

This patch solves a NULL pointer dereference, this may occur if the tuple is not mappable (jumps to continue in the for-loop).
Out of the loop possible results are: 
- info->list_size == 0  if no of the tuples is mappable
- info->list_size == 1
- info->list_size > 1
If no one of the supplied tuples is mappable (info->list_size == 0) and info->cmtd will not be set.
But it is used in mtd_device_parse_register, OOPS... if should generate an error in this case!

[From: Anton Prins <anton.prins@nl.bosch.com>]

From: Artem Bityutskiy [mailto:dedekind1@gmail.com] 
Sent: woensdag 21 november 2012 8:42
To: Prins Anton (ST-CO/ENG1.1)
Cc: linux-mtd@lists.infradead.org
Subject: Re: Patch to solve NULL pointer dereference in physmap_of.c
On Fri, 2012-11-09 at 08:45 +0100, Prins Anton (ST-CO/ENG1.1) wrote:
> commit 0905a6f4aec377123e94d2260f2f7a0d867e19be
> Author: Anton Prins <anton.prins@nl.bosch.com>
> Date:   Fri Nov 9 10:12:58 2012 +0100
> 
>     Correct error checking to prevent a NULL pointer dereference
> 
>     The problem only occurs if the DTS is not correct, the requested mapping is not reserved on the parent bus.
>     In this special case the count is 1, but the list_size after mapping is 0. list_size 0 should generate an error!

Sorry, I do not really understand which problem this patch solves, could
you please improve the commit message and re-send?

> 
> diff --git a/drivers/mtd/maps/physmap_of.c b/drivers/mtd/maps/physmap_of.c
> index 2e6fb68..83d121e 100644
> --- a/drivers/mtd/maps/physmap_of.c
> +++ b/drivers/mtd/maps/physmap_of.c
> @@ -267,13 +267,14 @@ static int __devinit of_flash_probe(struct platform_device *dev)
>                 info->list[i].mtd->dev.parent = &dev->dev;
>         }
> 

It seems the error condition should be checked and acted upon here. What
you looks more like making the code less readable.

> -       err = 0;
>         if (info->list_size == 1) {
> +               err = 0;
>                 info->cmtd = info->list[0].mtd;
>         } else if (info->list_size > 1) {
>                 /*
>                  * We detected multiple devices. Concatenate them together.
>                  */
> +               err = 0;
>                 info->cmtd = mtd_concat_create(mtd_list, info->list_size,
>                                                dev_name(&dev->dev));
>                 if (info->cmtd == NULL)


diff --git a/drivers/mtd/maps/physmap_of.c b/drivers/mtd/maps/physmap_of.c
index 2e6fb68..f6de444 100644
--- a/drivers/mtd/maps/physmap_of.c
+++ b/drivers/mtd/maps/physmap_of.c
@@ -268,6 +268,7 @@ static int __devinit of_flash_probe(struct platform_device *dev)
        }

        err = 0;
+       info->cmtd = NULL;
        if (info->list_size == 1) {
                info->cmtd = info->list[0].mtd;
        } else if (info->list_size > 1) {
@@ -276,9 +277,10 @@ static int __devinit of_flash_probe(struct platform_device *dev)
                 */
                info->cmtd = mtd_concat_create(mtd_list, info->list_size,
                                               dev_name(&dev->dev));
-               if (info->cmtd == NULL)
-                       err = -ENXIO;
        }
+       if (info->cmtd == NULL)
+               err = -ENXIO;
+
        if (err)
                goto err_out;

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