[v2] usbip: vhci_sysfs: fix potential Spectre v1

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

On Thu, May 17, 2018 at 03:16:28PM -0500, Gustavo A. R. Silva wrote:
> pdev_nr and rhport can be controlled by user-space, hence leading to
> a potential exploitation of the Spectre variant 1 vulnerability.
> 
> This issue was detected with the help of Smatch:
> drivers/usb/usbip/vhci_sysfs.c:238 detach_store() warn: potential spectre issue 'vhcis'
> drivers/usb/usbip/vhci_sysfs.c:328 attach_store() warn: potential spectre issue 'vhcis'
> drivers/usb/usbip/vhci_sysfs.c:338 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_ss->vdev'
> drivers/usb/usbip/vhci_sysfs.c:340 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_hs->vdev'
> 
> Fix this by sanitizing pdev_nr and rhport before using them to index
> vhcis and vhci->vhci_hcd_ss->vdev respectively.
> 
> Notice that given that speculation windows are large, the policy is
> to kill the speculation on the first load and not worry if it can be
> completed with a dependent load/store [1].
> 
> [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> Changes in v2:
>  - Place the barriers into valid_port.

Thanks for the change.  I'll wait for Shuah's ack/review before queueing
this up just as she knows that codebase much better than anyone else.

thanks,

greg k-h
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