Re: [PATCH] resource: make sure requested range intersects root range

[Ram Pai]

On Tue, Jul 10, 2012 at 02:33:48PM -0700, Andrew Morton wrote:
> On Sat, 30 Jun 2012 15:00:57 +0300
> Octavian Purdila <octavian.purdila@xxxxxxxxx> wrote:
> 
> > When the requested and root ranges do not intersect the logic in
> > __reserve_region_with_split will cause an infinite recursion which
> > will overflow the stack as seen in the warning bellow.
> > 
> > This particular stack overflow was caused by requesting the
> > (100000000-107ffffff) range while the root range was (0-ffffffff). In
> > this case __request_resource would return the whole root range as
> > conflict range (i.e. 0-ffffffff). Then, the logic in
> > __reserve_region_with_split would continue the recursion requesting
> > the new range as (conflict->end+1, end) which incidentally in this
> > case equals the originally requested range.
> > 
> > This patch aborts looking for a usable range when the requested one is
> > completely outside the root range to avoid the infinite recursion, and
> > since this indicates a problem in the layers above, it also prints an
> > error message indicating the requested and root range in order to make
> > the problem more easily traceable.
> 
> I think we should also emit a stack trace so the faulty caller can be
> pinpointed.
> 
> > ...
> >
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -789,7 +789,13 @@ void __init reserve_region_with_split(struct resource *root,
> >  		const char *name)
> >  {
> >  	write_lock(&resource_lock);
> > -	__reserve_region_with_split(root, start, end, name);
> > +	if (start > root->end || end < root->start)
> > +		pr_err("Requested range (0x%llx-0x%llx) not in root range (0x%llx-0x%llx)\n",
> > +		       (unsigned long long)start, (unsigned long long)end,
> > +		       (unsigned long long)root->start,
> > +		       (unsigned long long)root->end);
> > +	else
> > +		__reserve_region_with_split(root, start, end, name);
> >  	write_unlock(&resource_lock);
> >  }
> 
> The fancy way of doing that is
> 
> 	if (!WARN(start > root->end || end < root->start),
> 		  "Requested range (0x%llx-0x%llx) not in root range (0x%llx-0x%llx)\n",
> 		       (unsigned long long)start, (unsigned long long)end,
> 		       (unsigned long long)root->start,
> 		       (unsigned long long)root->end)
> 		__reserve_region_with_split(root, start, end, name);
> 
> but that's quite the eyesore.  How about doing it the simple way?
> 
> --- a/kernel/resource.c~resource-make-sure-requested-range-intersects-root-range-fix
> +++ a/kernel/resource.c
> @@ -792,13 +792,15 @@ void __init reserve_region_with_split(st
>  		const char *name)
>  {
>  	write_lock(&resource_lock);
> -	if (start > root->end || end < root->start)
> +	if (start > root->end || end < root->start) {
>  		pr_err("Requested range (0x%llx-0x%llx) not in root range (0x%llx-0x%llx)\n",
>  		       (unsigned long long)start, (unsigned long long)end,
>  		       (unsigned long long)root->start,
>  		       (unsigned long long)root->end);
> -	else
> +		dump_stack();
> +	} else {
>  		__reserve_region_with_split(root, start, end, name);
> +	}

Wait.. I am not sure this will fix the problem entirely. The above check
will handle the case where the range requested is entirey out of the
root's range.  But if the requested range overlapps that of the root
range, we will still call __reserve_region_with_split() and end up with 
a recursion if there is a overflow. Wont we?


>  	write_unlock(&resource_lock);
>  }
> 
RP

-- 
Ram Pai

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