[PATCH 3.16 49/99] usb: gadget: f_ncm: 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 5b24c28cfe136597dc3913e1c00b119307a20c7e upstream.

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")
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_ncm.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- a/drivers/usb/gadget/f_ncm.c
+++ b/drivers/usb/gadget/f_ncm.c
@@ -57,6 +57,7 @@ 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;
@@ -460,7 +461,7 @@ static void ncm_do_notify(struct f_ncm *
        int                             status;
 
        /* notification already in flight? */
-       if (!req)
+       if (atomic_read(&ncm->notify_count))
                return;
 
        event = req->buf;
@@ -500,7 +501,8 @@ static void ncm_do_notify(struct f_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,
@@ -510,7 +512,7 @@ static void ncm_do_notify(struct f_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);
        }
 }
@@ -545,17 +547,19 @@ static void ncm_notify_complete(struct u
        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);
 }
@@ -1382,6 +1386,11 @@ static void ncm_unbind(struct usb_config
 
        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);
 }