drm: stop information leak of old kernel stack.

commit b9f0aee83335db1f3915f4e42a5e21b351740afd upstream.

non-critical issue, CVE-2010-2803

Userspace controls the amount of memory to be allocate, so it can
get the ioctl to allocate more memory than the kernel uses, and get
access to kernel stack. This can only be done for processes authenticated
to the X server for DRI access, and if the user has DRI access.

Fix is to just memset the data to 0 if the user doesn't copy into
it in the first place.

Reported-by: Kees Cook <kees@ubuntu.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 452c2d866ec566e7355d065f7065518444ae289f..debeb8851bbcbe5bed1c008f6903a139a89f16c7 100644 (file)
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -504,7 +504,9 @@ int drm_ioctl(struct inode *inode, struct file *filp,
                                retcode = -EFAULT;
                                goto err_i1;
                        }
-               }
+               } else
+                       memset(kdata, 0, _IOC_SIZE(cmd));
+
                retcode = func(dev, kdata, file_priv);
 
                if ((retcode == 0) && (cmd & IOC_OUT)) {