[PATCH char-misc-linus] misc: mic: Fix for double fetch security bug in VOP driver

[Ashutosh Dixit]

The MIC VOP driver does two successive reads from user space to read a
variable length data structure. Kernel memory corruption can result if
the data structure changes between the two reads. This patch disallows
the chance of this happening.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116651
Reported by: Pengfei Wang <wpengfeinudt@xxxxxxxxx>
Reviewed-by: Sudeep Dutt <sudeep.dutt@xxxxxxxxx>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx>
---
 drivers/misc/mic/vop/vop_vringh.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/misc/mic/vop/vop_vringh.c b/drivers/misc/mic/vop/vop_vringh.c
index e94c7fb..88e4523 100644
--- a/drivers/misc/mic/vop/vop_vringh.c
+++ b/drivers/misc/mic/vop/vop_vringh.c
@@ -945,6 +945,11 @@ static long vop_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 			ret = -EFAULT;
 			goto free_ret;
 		}
+		/* Ensure desc has not changed between the two reads */
+		if (memcmp(&dd, dd_config, sizeof(dd))) {
+			ret = -EINVAL;
+			goto free_ret;
+		}
 		mutex_lock(&vdev->vdev_mutex);
 		mutex_lock(&vi->vop_mutex);
 		ret = vop_virtio_add_device(vdev, dd_config);
-- 
2.0.0.rc3.2.g998f840