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    Subject[PATCH 5.5 050/367] usb: gadget: f_ecm: Use atomic_t to track in-flight request
    Date
    From: Bryan O'Donoghue <bryan.odonoghue@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")
    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>

    ---
    drivers/usb/gadget/function/f_ecm.c | 16 ++++++++++++----
    1 file changed, 12 insertions(+), 4 deletions(-)

    --- a/drivers/usb/gadget/function/f_ecm.c
    +++ b/drivers/usb/gadget/function/f_ecm.c
    @@ -52,6 +52,7 @@ 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
    @@ -380,7 +381,7 @@ 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;
    @@ -420,10 +421,10 @@ 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);
    }
    }
    @@ -448,17 +449,19 @@ 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);
    }

    @@ -907,6 +910,11 @@ 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);
    }

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