[PATCH 3.16 50/99] usb: gadget: f_ecm: Use atomic_t to track in-flight request

[Ben Hutchings]

3.16.84-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Bryan O'Donoghue <bryan.odonog...@linaro.org>

commit d710562e01c48d59be3f60d58b7a85958b39aeda upstream.

Currently ecm->notify_req is used to flag when a request is in-flight.
ecm->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 ECM driver will
unconditionally free ecm->notify_req leading to a NULL pointer dereference.

Fixes: da741b8c56d6 ("usb ethernet gadget: split CDC Ethernet function")
Signed-off-by: Bryan O'Donoghue <bryan.odonog...@linaro.org>
Signed-off-by: Felipe Balbi <ba...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 drivers/usb/gadget/f_ecm.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

--- a/drivers/usb/gadget/f_ecm.c
+++ b/drivers/usb/gadget/f_ecm.c
@@ -56,6 +56,7 @@ struct f_ecm {
        struct usb_ep                   *notify;
        struct usb_request              *notify_req;
        u8                              notify_state;
+       atomic_t                        notify_count;
        bool                            is_open;
 
        /* FIXME is_open needs some irq-ish locking
@@ -384,7 +385,7 @@ static void ecm_do_notify(struct f_ecm *
        int                             status;
 
        /* notification already in flight? */
-       if (!req)
+       if (atomic_read(&ecm->notify_count))
                return;
 
        event = req->buf;
@@ -424,10 +425,10 @@ static void ecm_do_notify(struct f_ecm *
        event->bmRequestType = 0xA1;
        event->wIndex = cpu_to_le16(ecm->ctrl_id);
 
-       ecm->notify_req = NULL;
+       atomic_inc(&ecm->notify_count);
        status = usb_ep_queue(ecm->notify, req, GFP_ATOMIC);
        if (status < 0) {
-               ecm->notify_req = req;
+               atomic_dec(&ecm->notify_count);
                DBG(cdev, "notify --> %d\n", status);
        }
 }
@@ -452,17 +453,19 @@ static void ecm_notify_complete(struct u
        switch (req->status) {
        case 0:
                /* no fault */
+               atomic_dec(&ecm->notify_count);
                break;
        case -ECONNRESET:
        case -ESHUTDOWN:
+               atomic_set(&ecm->notify_count, 0);
                ecm->notify_state = ECM_NOTIFY_NONE;
                break;
        default:
                DBG(cdev, "event %02x --> %d\n",
                        event->bNotificationType, req->status);
+               atomic_dec(&ecm->notify_count);
                break;
        }
-       ecm->notify_req = req;
        ecm_do_notify(ecm);
 }
 
@@ -922,6 +925,11 @@ static void ecm_unbind(struct usb_config
 
        usb_free_all_descriptors(f);
 
+       if (atomic_read(&ecm->notify_count)) {
+               usb_ep_dequeue(ecm->notify, ecm->notify_req);
+               atomic_set(&ecm->notify_count, 0);
+       }
+
        kfree(ecm->notify_req->buf);
        usb_ep_free_request(ecm->notify, ecm->notify_req);
 }