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    Subject[PATCH 3.16 036/204] USB: gadgetfs: fix copy_to_user while holding spinlock
    3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Alan Stern <stern@rowland.harvard.edu>

    commit 6e76c01e71551cb221c1f3deacb9dcd9a7346784 upstream.

    The gadgetfs driver as a long-outstanding FIXME, regarding a call of
    copy_to_user() made while holding a spinlock. This patch fixes the
    issue by dropping the spinlock and using the dev->udc_usage mechanism
    introduced by another recent patch to guard against status changes
    while the lock isn't held.

    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    Reported-by: Andrey Konovalov <andreyknvl@google.com>
    Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    [bwh: Backported to 3.16: adjust filename]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/usb/gadget/inode.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/drivers/usb/gadget/inode.c
    +++ b/drivers/usb/gadget/inode.c
    @@ -1055,11 +1055,14 @@ ep0_read (struct file *fd, char __user *
    retval = -EIO;
    else {
    len = min (len, (size_t)dev->req->actual);
    -// FIXME don't call this with the spinlock held ...
    + ++dev->udc_usage;
    + spin_unlock_irq(&dev->lock);
    if (copy_to_user (buf, dev->req->buf, len))
    retval = -EFAULT;
    else
    retval = len;
    + spin_lock_irq(&dev->lock);
    + --dev->udc_usage;
    clean_req (dev->gadget->ep0, dev->req);
    /* NOTE userspace can't yet choose to stall */
    }
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