usbip: vhci_sysfs: fix potential Spectre v1

commit a0d6ec88090d7b1b008429c44532a388e29bb1bd upstream.

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>
Acked-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
index c287ccc..e8a008d 100644 (file)
--- a/drivers/usb/usbip/vhci_sysfs.c
+++ b/drivers/usb/usbip/vhci_sysfs.c
@@ -24,6 +24,9 @@
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 
+/* Hardening for Spectre-v1 */
+#include <linux/nospec.h>
+
 #include "usbip_common.h"
 #include "vhci.h"
 
@@ -181,16 +184,20 @@ static int vhci_port_disconnect(struct vhci_hcd *vhci, __u32 rhport)
        return 0;
 }
 
-static int valid_port(__u32 pdev_nr, __u32 rhport)
+static int valid_port(__u32 *pdev_nr, __u32 *rhport)
 {
-       if (pdev_nr >= vhci_num_controllers) {
-               pr_err("pdev %u\n", pdev_nr);
+       if (*pdev_nr >= vhci_num_controllers) {
+               pr_err("pdev %u\n", *pdev_nr);
                return 0;
        }
-       if (rhport >= VHCI_HC_PORTS) {
-               pr_err("rhport %u\n", rhport);
+       *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;
 }
 
@@ -207,7 +214,7 @@ static ssize_t store_detach(struct device *dev, struct device_attribute *attr,
        pdev_nr = port_to_pdev_nr(port);
        rhport = port_to_rhport(port);
 
-       if (!valid_port(pdev_nr, rhport))
+       if (!valid_port(&pdev_nr, &rhport))
                return -EINVAL;
 
        hcd = platform_get_drvdata(*(vhci_pdevs + pdev_nr));
@@ -226,7 +233,8 @@ static ssize_t store_detach(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR(detach, S_IWUSR, NULL, store_detach);
 
-static int valid_args(__u32 pdev_nr, __u32 rhport, enum usb_device_speed speed)
+static int valid_args(__u32 *pdev_nr, __u32 *rhport,
+                     enum usb_device_speed speed)
 {
        if (!valid_port(pdev_nr, rhport)) {
                return 0;
@@ -288,7 +296,7 @@ static ssize_t store_attach(struct device *dev, struct device_attribute *attr,
                             sockfd, devid, speed);
 
        /* check received parameters */
-       if (!valid_args(pdev_nr, rhport, speed))
+       if (!valid_args(&pdev_nr, &rhport, speed))
                return -EINVAL;
 
        hcd = platform_get_drvdata(*(vhci_pdevs + pdev_nr));