USB: cdc-wdm: fix buffer overflow

The buffer for responses must not overflow.
If this would happen, set a flag, drop the data and return
an error after user space has read all remaining data.

Signed-off-by: Oliver Neukum <oliver@neukum.org>
CC: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 20 insertions, 3 deletions

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 5f0cb417b736..122d056d96d5 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -56,6 +56,7 @@ MODULE_DEVICE_TABLE (usb, wdm_ids);
 #define WDM_RESPONDING          7
 #define WDM_SUSPENDING          8
 #define WDM_RESETTING           9
+#define WDM_OVERFLOW            10
 
 #define WDM_MAX                 16
 
@@ -155,6 +156,7 @@ static void wdm_in_callback(struct urb *urb)
 {
         struct wdm_device *desc = urb->context;
         int status = urb->status;
+        int length = urb->actual_length;
 
         spin_lock(&desc->iuspin);
         clear_bit(WDM_RESPONDING, &desc->flags);
@@ -185,9 +187,17 @@ static void wdm_in_callback(struct urb *urb)
         }
 
         desc->rerr = status;
-        desc->reslength = urb->actual_length;
-        memmove(desc->ubuf + desc->length, desc->inbuf, desc->reslength);
-        desc->length += desc->reslength;
+        if (length + desc->length > desc->wMaxCommand) {
+                /* The buffer would overflow */
+                set_bit(WDM_OVERFLOW, &desc->flags);
+        } else {
+                /* we may already be in overflow */
+                if (!test_bit(WDM_OVERFLOW, &desc->flags)) {
+                        memmove(desc->ubuf + desc->length, desc->inbuf, length);
+                        desc->length += length;
+                        desc->reslength = length;
+                }
+        }
 skip_error:
         wake_up(&desc->wait);
 
@@ -435,6 +445,11 @@ retry:
                         rv = -ENODEV;
                         goto err;
                 }
+                if (test_bit(WDM_OVERFLOW, &desc->flags)) {
+                        clear_bit(WDM_OVERFLOW, &desc->flags);
+                        rv = -ENOBUFS;
+                        goto err;
+                }
                 i++;
                 if (file->f_flags & O_NONBLOCK) {
                         if (!test_bit(WDM_READ, &desc->flags)) {
@@ -478,6 +493,7 @@ retry:
                         spin_unlock_irq(&desc->iuspin);
                         goto retry;
                 }
+
                 if (!desc->reslength) { /* zero length read */
                         dev_dbg(&desc->intf->dev, "%s: zero length - clearing WDM_READ\n", __func__);
                         clear_bit(WDM_READ, &desc->flags);
@@ -1004,6 +1020,7 @@ static int wdm_post_reset(struct usb_interface *intf)
         struct wdm_device *desc = wdm_find_device(intf);
         int rv;
 
+        clear_bit(WDM_OVERFLOW, &desc->flags);
         clear_bit(WDM_RESETTING, &desc->flags);
         rv = recover_from_urb_loss(desc);
         mutex_unlock(&desc->wlock);