[PATCH] usb: gadget: f_ncm: Prevent use-after-free of notify_req

["Kieronski, Milosz" <milosz.kieronski@xxxxxxxxx>]

When ncm_ubind() executes first then ncm->notify_req is freed before
usb_ep_free_request(). This produces use-after-free bug in ncm_close()
while we write to ncm->notify_req->buf despite the "if (!req)".

To make this sanity check working, we set ncm->notify_req to NULL
after each free.

Signed-off-by: Milosz Kieronski <milosz.kieronski@xxxxxxxxx>
Co-developed-by: Slawek Ignacyk <slawek.ignacyk@xxxxxxxxx>
Signed-off-by: Slawek Ignacyk <slawek.ignacyk@xxxxxxxxx>
---
 drivers/usb/gadget/function/f_ncm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index 2d6e76e4cffa..a1a521a69187 100644
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -1526,10 +1526,13 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 	kfree(f->os_desc_table);
 	f->os_desc_n = 0;
 
+	spin_lock(&ncm->lock);
 	if (ncm->notify_req) {
 		kfree(ncm->notify_req->buf);
 		usb_ep_free_request(ncm->notify, ncm->notify_req);
+		ncm->notify_req = NULL;
 	}
+	spin_unlock(&ncm->lock);
 
 	ERROR(cdev, "%s: can't bind, err %d\n", f->name, status);
 
@@ -1649,8 +1652,11 @@ static void ncm_unbind(struct usb_configuration *c, struct usb_function *f)
 	ncm_string_defs[0].id = 0;
 	usb_free_all_descriptors(f);
 
+	spin_lock(&ncm->lock);
 	kfree(ncm->notify_req->buf);
 	usb_ep_free_request(ncm->notify, ncm->notify_req);
+	ncm->notify_req = NULL;
+	spin_unlock(&ncm->lock);
 }
 
 static struct usb_function *ncm_alloc(struct usb_function_instance *fi)
-- 
2.17.1