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    Subject[066/104] Staging: comedi: fix mmap_count
    3.1-stable review patch.  If anyone has any objections, please let me know.

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

    From: Federico Vaga <federico.vaga@gmail.com>

    commit df30b21cb0eed5ba8a8e0cdfeebc66ba8cde821d upstream.

    In comedi_fops, mmap_count is decremented at comedi_vm_ops->close but
    it is not incremented at comedi_vm_ops->open. This may result in a negative
    counter. The patch introduces the open method to keep the counter
    consistent.

    The bug was triggerd by this sample code:

    mmap(0, ...., comedi_fd);
    fork();
    exit(0);

    Acked-by: Alessandro Rubini <rubini@gnudd.com>
    Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/staging/comedi/comedi_fops.c | 19 +++++++++++++++++--
    1 file changed, 17 insertions(+), 2 deletions(-)

    --- a/drivers/staging/comedi/comedi_fops.c
    +++ b/drivers/staging/comedi/comedi_fops.c
    @@ -1432,7 +1432,21 @@ static int do_cancel(struct comedi_devic
    return ret;
    }

    -static void comedi_unmap(struct vm_area_struct *area)
    +
    +static void comedi_vm_open(struct vm_area_struct *area)
    +{
    + struct comedi_async *async;
    + struct comedi_device *dev;
    +
    + async = area->vm_private_data;
    + dev = async->subdevice->device;
    +
    + mutex_lock(&dev->mutex);
    + async->mmap_count++;
    + mutex_unlock(&dev->mutex);
    +}
    +
    +static void comedi_vm_close(struct vm_area_struct *area)
    {
    struct comedi_async *async;
    struct comedi_device *dev;
    @@ -1446,7 +1460,8 @@ static void comedi_unmap(struct vm_area_
    }

    static struct vm_operations_struct comedi_vm_ops = {
    - .close = comedi_unmap,
    + .open = comedi_vm_open,
    + .close = comedi_vm_close,
    };

    static int comedi_mmap(struct file *file, struct vm_area_struct *vma)



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