[PATCH] drm: fix NULL pointer access by wrong ioctl

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/1797546

If user uses wrong ioctl command with _IOC_NONE and argument size
greater than 0, it can cause NULL pointer access from memset of line
463. If _IOC_NONE, don't memset to 0 for kdata.

Signed-off-by: Zhaowei Yuan <zhaowei.yuan at samsung.com>
Reviewed-by: David Herrmann <dh.herrmann at gmail.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Dave Airlie <airlied at redhat.com>
(backported from commit 1539fb9bd405ee32282ea0a38404f9e008ac5b7a)
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 drivers/gpu/drm/drm_drv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index d9137e4..ef65779 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -383,8 +383,9 @@ long drm_ioctl(struct file *filp,
 				retcode = -EFAULT;
 				goto err_i1;
 			}
-		} else
+		} else if (cmd & IOC_OUT) {
 			memset(kdata, 0, usize);
+		}
 
 		if (ioctl->flags & DRM_UNLOCKED)
 			retcode = func(dev, kdata, file_priv);
-- 
1.9.1