staging: comedi: don't allow write() on async command set up for "read"

If a Comedi asynchronous command has been set up for data transfer in
the "read" direction on the current "write" subdevice (for those
subdevices that support both directions), don't allow the "write" file
operation as that would mess with the data in the comedi data buffer
that is written by the low-level comedi hardware driver.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 452121b6a604f50a5cf9a7ea9acb21d7fe07172b..0ed6f1f00e7fc875fdb7e9c8775478c60ed709ef 100644 (file)
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2075,6 +2075,10 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
                retval = -EACCES;
                goto out;
        }
+       if (!(async->cmd.flags & CMDF_WRITE)) {
+               retval = -EINVAL;
+               goto out;
+       }
 
        add_wait_queue(&async->wait_head, &wait);
        on_wait_queue = true;
@@ -2146,6 +2150,10 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
                                retval = -EACCES;
                                break;
                        }
+                       if (!(async->cmd.flags & CMDF_WRITE)) {
+                               retval = -EINVAL;
+                               break;
+                       }
                        continue;
                }