Re: [PATCH] mm/vmalloc: Sanitize __get_vm_area() arguments

[Christoph Hellwig]

On Fri, Apr 03, 2020 at 06:32:53PM +0200, Peter Zijlstra wrote:
> 
> __get_vm_area() is an exported symbol, make sure the callers stay in
> the expected memory range. When calling this function with memory
> ranges outside of the VMALLOC range *bad* things can happen.
> 
> (I noticed this when I managed to corrupt the kernel text by accident)

Maybe it is time to unexport it?  There are only two users:

 - staging/media/ipu3 really should be using vmap.  And given that it
   is a staging driver it really doesn't matter anyway if we break it.
 - pcmcia/electra_cf.c is actually using it for something that is not
   a vmalloc address.  But it is so special that I think prohibiting
   to build it as module seems fine.

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  mm/vmalloc.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2130,6 +2130,13 @@ static struct vm_struct *__get_vm_area_n
>  struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
>  				unsigned long start, unsigned long end)
>  {
> +	/*
> +	 * Ensure callers stay in the vmalloc range.
> +	 */
> +	if (WARN_ON(start < VMALLOC_START || start > VMALLOC_END ||
> +		    end < VMALLOC_START || end > VMALLOC_END))
> +		return NULL;
> +
>  	return __get_vm_area_node(size, 1, flags, start, end, NUMA_NO_NODE,
>  				  GFP_KERNEL, __builtin_return_address(0));
>  }
---end quoted text---