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SubjectRe: [PATCH 1/3] drivers/gpu/drm: Move a dereference below a NULL test
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On Sat, 2008-12-20 at 08:35 +1000, Dave Airlie wrote:
> On Sat, Dec 20, 2008 at 3:10 AM, Julia Lawall <julia@diku.dk> wrote:
> > From: Julia Lawall <julia@diku.dk>
> >
> > If the NULL test is necessary, then the dereference should be moved below
> > the NULL test.
> >
> > The semantic patch that makes this change is as follows:
> > (http://www.emn.fr/x-info/coccinelle/). The result has been modified to
> > move the initialization of driver down closer to where it is used.
> >
> > // <smpl>
> > @@
> > type T;
> > expression E;
> > identifier i,fld;
> > statement S;
> > @@
> >
> > - T i = E->fld;
> > + T i;
> > ... when != E
> > when != i
> > if (E == NULL) S
> > + i = E->fld;
> > // </smpl>
> >
> > Signed-off-by: Julia Lawall <julia@diku.dk>
> >
> > ---
> > drivers/gpu/drm/drm_drv.c | 7 ++++---
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index 0b9f316..4bdfc98 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -297,7 +297,7 @@ EXPORT_SYMBOL(drm_init);
> > */
> > static void drm_cleanup(struct drm_device * dev)
> > {
> > - struct drm_driver *driver = dev->driver;
> > + struct drm_driver *driver;
> >
> > DRM_DEBUG("\n");
> >
> > @@ -324,8 +324,9 @@ static void drm_cleanup(struct drm_device * dev)
> > dev->agp = NULL;
> > }
> >
> > - if (dev->driver->unload)
> > - dev->driver->unload(dev);
> > + driver = dev->driver;
> > + if (driver->unload)
> > + driver->unload(dev);
>
> Huh?
>
> The original test is to check it dev->driver->unload exists, not it
> dev->driver exists.
>
> I think your test parameters are wrong.

No, it was valid, but I think the better patch is:

From 1e0a24cfe75a328db5a50dbcdaaf0eb461638b6b Mon Sep 17 00:00:00 2001
From: Eric Anholt <eric@anholt.net>
Date: Fri, 19 Dec 2008 15:07:11 -0800
Subject: [PATCH] drm: Avoid use-before-null-test on dev in drm_cleanup().

Signed-off-by: Eric Anholt <eric@anholt.net>

---
drivers/gpu/drm/drm_drv.c | 4 +---
1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 373e3de..febb517 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -294,8 +294,6 @@ EXPORT_SYMBOL(drm_init);
*/
static void drm_cleanup(struct drm_device * dev)
{
- struct drm_driver *driver = dev->driver;
-
DRM_DEBUG("\n");

if (!dev) {
@@ -330,7 +328,7 @@ static void drm_cleanup(struct drm_device * dev)
if (drm_core_check_feature(dev, DRIVER_MODESET))
drm_put_minor(&dev->control);

- if (driver->driver_features & DRIVER_GEM)
+ if (dev->driver->driver_features & DRIVER_GEM)
drm_gem_destroy(dev);

drm_put_minor(&dev->primary);
--
1.5.6.5

--
Eric Anholt
eric@anholt.net eric.anholt@intel.com


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