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 
drivers/usb/usbip/vhci_sysfs.c:328 attach_store() warn: potential spectre issue 
drivers/usb/usbip/vhci_sysfs.c:338 attach_store() warn: potential spectre issue 
drivers/usb/usbip/vhci_sysfs.c:340 attach_store() warn: potential spectre issue 

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: sta...@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com>
Changes in v2:
 - Place the barriers into valid_port.

 drivers/usb/usbip/vhci_sysfs.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
index 4880838..69db0c9 100644
--- a/drivers/usb/usbip/vhci_sysfs.c
+++ b/drivers/usb/usbip/vhci_sysfs.c
@@ -10,6 +10,8 @@
 #include <linux/platform_device.h>
 #include <linux/slab.h>
+#include <linux/nospec.h>
 #include "usbip_common.h"
 #include "vhci.h"
@@ -211,10 +213,14 @@ static int valid_port(__u32 pdev_nr, __u32 rhport)
                pr_err("pdev %u\n", pdev_nr);
                return 0;
+       pdev_nr = array_index_nospec(pdev_nr, vhci_num_controllers);
        if (rhport >= VHCI_HC_PORTS) {
                pr_err("rhport %u\n", rhport);
                return 0;
+       rhport = array_index_nospec(rhport, VHCI_HC_PORTS);
        return 1;

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