Re: KASAN: slab-out-of-bounds Read in handle_vmptrld

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Sep 13, 2019 at 09:34:32AM +0200, Paolo Bonzini wrote:
> On 13/09/19 06:46, Greg Kroah-Hartman wrote:
> > USB drivers expect kmalloc to return DMA-able memory.  I don't know
> > about specific alignment issues, that should only an issue for the host
> > controller being used here, which you do not say in the above list.
> 
> I have no idea, this is just the analysis of a syzkaller report.  From 
> the backtrace, it's one that ends up calling kmalloc; all of them should
> have the same issue with KASAN.
> 
> The specific alignment requirement for this bug comes from this call in
> usbdev_mmap:
> 
> 	if (remap_pfn_range(vma, vma->vm_start,
> 			virt_to_phys(usbm->mem) >> PAGE_SHIFT,
> 			size, vma->vm_page_prot) < 0) {
> 
> > We have had some reports that usbdev_mmap() does not do the "correct
> > thing" for all host controllers, but a lot of the DMA work that is in
> > linux-next for 5.4-rc1 should have helped resolve those issues.  What
> > tree are you seeing these bug reports happening from?
> 
> It's in master, but the relevant code is the same in linux-next; in fact
> in this case there is no DMA involved at all.  hcd_buffer_alloc hits
> the case "some USB hosts just use PIO".
> 
> On those host controllers, it should be reproducible with just this:
> 
> diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
> index 7fcb9f782931..cc0460730bce 100644
> --- a/drivers/usb/core/usb.c
> +++ b/drivers/usb/core/usb.c
> @@ -905,9 +905,12 @@ EXPORT_SYMBOL_GPL(__usb_get_extra_descriptor);
>  void *usb_alloc_coherent(struct usb_device *dev, size_t size, gfp_t mem_flags,
>  			 dma_addr_t *dma)
>  {
> +	void *buf;
>  	if (!dev || !dev->bus)
>  		return NULL;
> -	return hcd_buffer_alloc(dev->bus, size, mem_flags, dma);
> +	buf = hcd_buffer_alloc(dev->bus, size, mem_flags, dma);
> +	WARN_ON_ONCE(virt_to_phys(buf) & ~PAGE_MASK);
> +	return buf;
>  }
>  EXPORT_SYMBOL_GPL(usb_alloc_coherent);

Look at linux-next, we "should" have fixed up hcd_buffer_alloc() now to
not need this type of thing.  If we got it wrong, please let us know and
then yes, a fix like this would be most appreciated :)

thanks,

greg k-h

>  
> 
> and CONFIG_KASAN=y or possibly just CONFIG_DEBUG_SLAB=y.  mmap-ing /dev/usb
> should warn if my analysis is correct.
> 
> If you think the above patch makes sense, I can test it and submit it formally.
> 
> Paolo

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