usb: gadget: f_ncm: Use atomic_t to track in-flight request

Currently ncm->notify_req is used to flag when a request is in-flight.
ncm->notify_req is set to NULL and when a request completes it is
subsequently reset.

This is fundamentally buggy in that the unbind logic of the NCM driver will
unconditionally free ncm->notify_req leading to a NULL pointer dereference.

Fixes: 40d133d7f542 ("usb: gadget: f_ncm: convert to new function interface with backward compatibility")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index 2d6e76e4cffad6b3929809c1f8d876477439c76c..1d900081b1f0ca5e5e01b24d701d1cd7a1459a9f 100644 (file)
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -53,6 +53,7 @@ struct f_ncm {
        struct usb_ep                   *notify;
        struct usb_request              *notify_req;
        u8                              notify_state;
+       atomic_t                        notify_count;
        bool                            is_open;
 
        const struct ndp_parser_opts    *parser_opts;
@@ -547,7 +548,7 @@ static void ncm_do_notify(struct f_ncm *ncm)
        int                             status;
 
        /* notification already in flight? */
-       if (!req)
+       if (atomic_read(&ncm->notify_count))
                return;
 
        event = req->buf;
@@ -587,7 +588,8 @@ static void ncm_do_notify(struct f_ncm *ncm)
        event->bmRequestType = 0xA1;
        event->wIndex = cpu_to_le16(ncm->ctrl_id);
 
-       ncm->notify_req = NULL;
+       atomic_inc(&ncm->notify_count);
+
        /*
         * In double buffering if there is a space in FIFO,
         * completion callback can be called right after the call,
@@ -597,7 +599,7 @@ static void ncm_do_notify(struct f_ncm *ncm)
        status = usb_ep_queue(ncm->notify, req, GFP_ATOMIC);
        spin_lock(&ncm->lock);
        if (status < 0) {
-               ncm->notify_req = req;
+               atomic_dec(&ncm->notify_count);
                DBG(cdev, "notify --> %d\n", status);
        }
 }
@@ -632,17 +634,19 @@ static void ncm_notify_complete(struct usb_ep *ep, struct usb_request *req)
        case 0:
                VDBG(cdev, "Notification %02x sent\n",
                     event->bNotificationType);
+               atomic_dec(&ncm->notify_count);
                break;
        case -ECONNRESET:
        case -ESHUTDOWN:
+               atomic_set(&ncm->notify_count, 0);
                ncm->notify_state = NCM_NOTIFY_NONE;
                break;
        default:
                DBG(cdev, "event %02x --> %d\n",
                        event->bNotificationType, req->status);
+               atomic_dec(&ncm->notify_count);
                break;
        }
-       ncm->notify_req = req;
        ncm_do_notify(ncm);
        spin_unlock(&ncm->lock);
 }
@@ -1649,6 +1653,11 @@ static void ncm_unbind(struct usb_configuration *c, struct usb_function *f)
        ncm_string_defs[0].id = 0;
        usb_free_all_descriptors(f);
 
+       if (atomic_read(&ncm->notify_count)) {
+               usb_ep_dequeue(ncm->notify, ncm->notify_req);
+               atomic_set(&ncm->notify_count, 0);
+       }
+
        kfree(ncm->notify_req->buf);
        usb_ep_free_request(ncm->notify, ncm->notify_req);
 }