Re: [PATCH v3 1/4] kernel/resource: Invalid memory access in __release_resource

[Bjorn Helgaas <bhelgaas@google.com>]

On Wed, Apr 22, 2015 at 06:14:18PM +0200, Ricardo Ribalda Delgado wrote:
> When a resource is initialized via of_platform_populate.
> resource->parent is initialized to NULL via kzalloc.
> (of_platform_populate->of_device_alloc->of_address_to_resource)
> 
> If of_platform_depopulate is called later, resource->parent is
> accessed (Offset 0x30 of address 0), causing a kernel error.
> 
> This patch evaluates resouce->parent before accessing it. If it
> is not initialized, -EACCESS is returned.
> 
> Also a WARN is thrown, so the developer can have a hint about what
> needs to be fixed.
> 
> Fixes:
> BUG: unable to handle kernel NULL pointer deference at 0000000000000030
> IP: release_resource+0x26/0x90
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
> ---
>  kernel/resource.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 90552aa..b7b270f 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -237,6 +237,9 @@ static int __release_resource(struct resource *old)
>  {
>  	struct resource *tmp, **p;
>  
> +	if (WARN_ON(!old->parent))
> +		return -EINVAL;

I'm not really a fan of this.  The NULL pointer oops is a very good clue
all by itself, and it doesn't require any extra code here.

>  	p = &old->parent->child;
>  	for (;;) {
>  		tmp = *p;
> -- 
> 2.1.4
>