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@xxxxxxxxx>
Signed-off-by: Federico Vaga <federico.vaga@xxxxxxxxx>
---
drivers/staging/comedi/comedi_fops.c | 19 +++++++++++++++++--
1 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 21d8c1c..173242c 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -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)
--
1.5.6.5
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