Messages in this thread | | | Date | Mon, 20 Apr 2015 14:28:44 -0500 | From | Bjorn Helgaas <> | Subject | Re: [PATCH] kernel/resource: Invalid memory access in __release_resource |
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[+cc Grant (author of ac80a51e2ce5)]
Hi Ricardo,
On Mon, Apr 20, 2015 at 06:22:52PM +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.
Interesting; how'd you find this? It looks like the of_platform_depopulate() code has been this way for a long time, so we must be doing something new that makes us trip over this now. More analysis below...
> This patch evaluates resouce->parent before accessing it. If it > is not initialized, -EACCESS is returned. > > 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..35dc716 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 (!old->parent) > + return -EINVAL;
This path has been fine for a long time without testing for a NULL pointer, so I suspect this change papers over an issue that would be better fixed elsewhere.
From reading drivers/base/platform.c, it looks like the intent is that platform device users would use these interfaces:
- platform_device_alloc()
- platform_device_add_resources(platform_device *pdev) pdev->num_resources = num
- platform_device_add(platform_device *pdev) for (i = 0; i < pdev->num_resources; i++) insert_resource() device_add(&pdev->dev)
- platform_device_unregister(platform_device *pdev) platform_device_del(platform_device *pdev) for (i = 0; i < pdev->num_resources; i++) release_resource()
Resources are added by platform_device_add_resources() and inserted into the resource tree by platform_device_add(). In this usage, resources are removed from the resource tree by platform_device_unregister(), and there's no issue with resource->parent being NULL.
OF uses platform_device_alloc() and platform_device_unregister(), but not platform_device_add(). It doesn't call insert_resource(), and that breaks the platform_device_unregister() assumption that the resources are in the resource tree:
- of_platform_populate() ... of_device_alloc() pdev = platform_device_alloc() # set pdev->resource, similar to platform_device_add_resources() of_device_add(platform_device *pdev) # similar to platform_device_add(), but note there's no # insert_resource() in this path device_add(&pdev->dev)
- of_platform_depopulate() of_platform_device_destroy() platform_device_unregister(platform_device *pdev) platform_device_del(platform_device *pdev) for (i = 0; i < pdev->num_resources; i++) release_resource()
I cc'd Grant because ac80a51e2ce5 ("of/device: populate platform_device (of_device) resource table on allocation") added the pdev->resource management in of_device_alloc(), so maybe he has more insight into this.
> p = &old->parent->child; > for (;;) { > tmp = *p; > -- > 2.1.4 >
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