usb: gadget: composite: Fix possible double free memory bug

composite_dev_cleanup call from the failure of configfs_composite_bind
frees up the cdev->os_desc_req and cdev->req. If the previous calls of
bind and unbind is successful these will carry stale values.

Consider the below sequence of function calls:
configfs_composite_bind()
        composite_dev_prepare()
                - Allocate cdev->req, cdev->req->buf
        composite_os_desc_req_prepare()
                - Allocate cdev->os_desc_req, cdev->os_desc_req->buf
configfs_composite_unbind()
        composite_dev_cleanup()
                - free the cdev->os_desc_req->buf and cdev->req->buf
Next composition switch
configfs_composite_bind()
        - If it fails goto err_comp_cleanup will call the
	  composite_dev_cleanup() function
        composite_dev_cleanup()
	        - calls kfree up with the stale values of cdev->req->buf and
		  cdev->os_desc_req from the previous configfs_composite_bind
		  call. The free call on these stale values leads to double free.

Hence, Fix this issue by setting request and buffer pointer to NULL after
kfree.

Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index d516e8d..5ec54b6 100644 (file)
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -2170,14 +2170,18 @@ void composite_dev_cleanup(struct usb_composite_dev *cdev)
                        usb_ep_dequeue(cdev->gadget->ep0, cdev->os_desc_req);
 
                kfree(cdev->os_desc_req->buf);
+               cdev->os_desc_req->buf = NULL;
                usb_ep_free_request(cdev->gadget->ep0, cdev->os_desc_req);
+               cdev->os_desc_req = NULL;
        }
        if (cdev->req) {
                if (cdev->setup_pending)
                        usb_ep_dequeue(cdev->gadget->ep0, cdev->req);
 
                kfree(cdev->req->buf);
+               cdev->req->buf = NULL;
                usb_ep_free_request(cdev->gadget->ep0, cdev->req);
+               cdev->req = NULL;
        }
        cdev->next_string_id = 0;
        device_remove_file(&cdev->gadget->dev, &dev_attr_suspended);