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Staging: comedi: fix mmap_count

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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>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Federico Vaga 2011-10-29 09:45:39 +02:00 committed by Greg Kroah-Hartman
parent 3ffab428f4
commit df30b21cb0
1 changed files with 17 additions and 2 deletions
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19
drivers/staging/comedi/comedi_fops.c
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@ -1432,7 +1432,21 @@ static int do_cancel(struct comedi_device *dev, struct comedi_subdevice *s)
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_struct *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)