[PATCH 4.9 106/153] usb: gadget: f_hid: fix: Prevent accessing released memory

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Krzysztof Opasiak <kopasiak90@xxxxxxxxx>

commit aa65d11aa008f4de58a9cee7e121666d9d68505e upstream.

When we unlock our spinlock to copy data to user we may get
disabled by USB host and free the whole list of completed out
requests including the one from which we are copying the data
to user memory.

To prevent from this let's remove our working element from
the list and place it back only if there is sth left when we
finish with it.

Fixes: 99c515005857 ("usb: gadget: hidg: register OUT INT endpoint for SET_REPORT")
Tested-by: David Lechner <david@xxxxxxxxxxxxxx>
Signed-off-by: Krzysztof Opasiak <k.opasiak@xxxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/gadget/function/f_hid.c |   24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

--- a/drivers/usb/gadget/function/f_hid.c
+++ b/drivers/usb/gadget/function/f_hid.c
@@ -223,6 +223,13 @@ static ssize_t f_hidg_read(struct file *
 	/* pick the first one */
 	list = list_first_entry(&hidg->completed_out_req,
 				struct f_hidg_req_list, list);
+
+	/*
+	 * Remove this from list to protect it from beign free()
+	 * while host disables our function
+	 */
+	list_del(&list->list);
+
 	req = list->req;
 	count = min_t(unsigned int, count, req->actual - list->pos);
 	spin_unlock_irqrestore(&hidg->spinlock, flags);
@@ -238,15 +245,20 @@ static ssize_t f_hidg_read(struct file *
 	 * call, taking into account its current read position.
 	 */
 	if (list->pos == req->actual) {
-		spin_lock_irqsave(&hidg->spinlock, flags);
-		list_del(&list->list);
 		kfree(list);
-		spin_unlock_irqrestore(&hidg->spinlock, flags);
 
 		req->length = hidg->report_length;
 		ret = usb_ep_queue(hidg->out_ep, req, GFP_KERNEL);
-		if (ret < 0)
+		if (ret < 0) {
+			free_ep_req(hidg->out_ep, req);
 			return ret;
+		}
+	} else {
+		spin_lock_irqsave(&hidg->spinlock, flags);
+		list_add(&list->list, &hidg->completed_out_req);
+		spin_unlock_irqrestore(&hidg->spinlock, flags);
+
+		wake_up(&hidg->read_queue);
 	}
 
 	return count;
@@ -506,14 +518,18 @@ static void hidg_disable(struct usb_func
 {
 	struct f_hidg *hidg = func_to_hidg(f);
 	struct f_hidg_req_list *list, *next;
+	unsigned long flags;
 
 	usb_ep_disable(hidg->in_ep);
 	usb_ep_disable(hidg->out_ep);
 
+	spin_lock_irqsave(&hidg->spinlock, flags);
 	list_for_each_entry_safe(list, next, &hidg->completed_out_req, list) {
+		free_ep_req(hidg->out_ep, list->req);
 		list_del(&list->list);
 		kfree(list);
 	}
+	spin_unlock_irqrestore(&hidg->spinlock, flags);
 }
 
 static int hidg_set_alt(struct usb_function *f, unsigned intf, unsigned alt)