staging: comedi: comedi_compat32.c: fix COMEDI_CMD copy back

`do_cmd_ioctl()` in "comedi_fops.c" handles the `COMEDI_CMD` ioctl.
This returns `-EAGAIN` if it has copied a modified `struct comedi_cmd`
back to user-space.  (This occurs when the low-level Comedi driver's
`do_cmdtest()` handler returns non-zero to indicate a problem with the
contents of the `struct comedi_cmd`, or when the `struct comedi_cmd` has
the `CMDF_BOGUS` flag set.)

`compat_cmd()` in "comedi_compat32.c" handles the 32-bit compatible
version of the `COMEDI_CMD` ioctl.  Currently, it never copies a 32-bit
compatible version of `struct comedi_cmd` back to user-space, which is
at odds with the way the regular `COMEDI_CMD` ioctl is handled.  To fix
it, change `compat_cmd()` to copy a 32-bit compatible version of the
`struct comedi_cmd` back to user-space when the main ioctl handler
returns `-EAGAIN`.

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

diff --git a/drivers/staging/comedi/comedi_compat32.c b/drivers/staging/comedi/comedi_compat32.c
index 5a4c74f..03a2d07 100644 (file)
--- a/drivers/staging/comedi/comedi_compat32.c
+++ b/drivers/staging/comedi/comedi_compat32.c
@@ -262,7 +262,7 @@ static int compat_cmd(struct file *file, unsigned long arg)
 {
        struct comedi_cmd __user *cmd;
        struct comedi32_cmd_struct __user *cmd32;
-       int rc;
+       int rc, err;
 
        cmd32 = compat_ptr(arg);
        cmd = compat_alloc_user_space(sizeof(*cmd));
@@ -271,7 +271,15 @@ static int compat_cmd(struct file *file, unsigned long arg)
        if (rc)
                return rc;
 
-       return translated_ioctl(file, COMEDI_CMD, (unsigned long)cmd);
+       rc = translated_ioctl(file, COMEDI_CMD, (unsigned long)cmd);
+       if (rc == -EAGAIN) {
+               /* Special case: copy cmd back to user. */
+               err = put_compat_cmd(cmd32, cmd);
+               if (err)
+                       rc = err;
+       }
+
+       return rc;
 }
 
 /* Handle 32-bit COMEDI_CMDTEST ioctl. */