Re: [PATCH 1/7] staging: comedi: comedi_compat32.c: fix COMEDI_CMD copy back

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On 27/01/15 15:50, Ian Abbott wrote:
`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@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
  drivers/staging/comedi/comedi_compat32.c | 13 +++++++++++--
  1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/comedi/comedi_compat32.c b/drivers/staging/comedi/comedi_compat32.c
index 5a4c74f..2440c60 100644
--- a/drivers/staging/comedi/comedi_compat32.c
+++ b/drivers/staging/comedi/comedi_compat32.c
@@ -262,7 +262,8 @@ static int compat_cmd(struct file *file, unsigned long arg)
  {
  	struct comedi_cmd __user *cmd;
  	struct comedi32_cmd_struct __user *cmd32;
-	int rc;
+	long rc;
+	int err;

Gah! That change in type of the 'rc' variable resulted from me changing the order of the patches in the series. It still works, but looks a bit out of place. Should I post an updated version without this niggle?


  	cmd32 = compat_ptr(arg);
  	cmd = compat_alloc_user_space(sizeof(*cmd));
@@ -271,7 +272,15 @@ 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. */



--
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@xxxxxxxxx> )=-
-=(                          Web: http://www.mev.co.uk/  )=-
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