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

If a Comedi asynchronous command has been set up for data transfer in
the "write" direction on the current "read" subdevice (for those
subdevices that support both directions), don't allow the "read" file
operation as that would mess with the data in the comedi data buffer
that is read 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 b489d9481a695da280ed5e4cf7780223f8af91a2..452121b6a604f50a5cf9a7ea9acb21d7fe07172b 100644 (file)
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2210,6 +2210,10 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
                retval = -EACCES;
                goto out;
        }
+       if (async->cmd.flags & CMDF_WRITE) {
+               retval = -EINVAL;
+               goto out;
+       }
 
        add_wait_queue(&async->wait_head, &wait);
        while (nbytes > 0 && !retval) {
@@ -2249,6 +2253,10 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
                                retval = -EACCES;
                                break;
                        }
+                       if (async->cmd.flags & CMDF_WRITE) {
+                               retval = -EINVAL;
+                               break;
+                       }
                        continue;
                }
                m = copy_to_user(buf, async->prealloc_buf +