linux-kernel - [PATCH 3.19 133/177] staging: comedi: comedi_compat32.c: fix COMEDI

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Message-Id: <20150316140819.145656239@linuxfoundation.org>
Date:	Mon, 16 Mar 2015 15:09:00 +0100
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Ian Abbott <abbotti@....co.uk>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>
Subject: [PATCH 3.19 133/177] staging: comedi: comedi_compat32.c: fix COMEDI_CMD copy back

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ian Abbott <abbotti@....co.uk>

commit 42b8ce6f55facfa101462e694d33fc6bca471138 upstream.

`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@....co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@...ionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/staging/comedi/comedi_compat32.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- 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,
 {
 	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,
 	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. */

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