[47/80] Staging: comedi: fix mmap_count

Greg KH
2011-12-07T16:18:02Z

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)