linux-kernel - Re: [PATCH] resource: Add NULL check in next

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Message-ID: <20140922145704.GC4250@redhat.com>
Date:	Mon, 22 Sep 2014 10:57:04 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mikael Starvik <starvik@...s.com>,
	Jesper Nilsson <jesper.nilsson@...s.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] resource: Add NULL check in next_resource

On Sun, Sep 21, 2014 at 08:51:44AM -0700, Guenter Roeck wrote:
> Commit 8c86e70acead ("resource: provide new functions to walk through
> resources") adds a suble new requirement that iomem_resource.child must
> not be NULL when walk_system_ram_range is called. This can cause a crash
> if it turns out that there are no children. The crash ('Unable to handle
> kernel NULL pointer dereference') is seen when trying to test a crisv32
> image on kernels with this commit applied.
> 
> Fix by adding a NULL check into next_resource().
> 
> Fixes: 8c86e70acead ("resource: provide new functions to walk through resources")

Hi Guenter,

Can you please provide backtrace of the crash.

Thanks
Vivek

> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> The NULL check could be added elsewhere instead. I am open to suggestions.
> 
>  kernel/resource.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 60c5a38..00c57ad 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -61,6 +61,9 @@ static DEFINE_SPINLOCK(bootmem_resource_lock);
>  
>  static struct resource *next_resource(struct resource *p, bool sibling_only)
>  {
> +	if (p == NULL)
> +		return NULL;
> +
>  	/* Caller wants to traverse through siblings only */
>  	if (sibling_only)
>  		return p->sibling;
> -- 
> 1.9.1
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