vhost: fix info leak due to uninitialized memory

CVE-2018-1118

struct vhost_msg within struct vhost_msg_node is copied to userspace.
Unfortunately it turns out on 64 bit systems vhost_msg has padding after
type which gcc doesn't initialize, leaking 4 uninitialized bytes to
userspace.

This padding also unfortunately means 32 bit users of this interface are
broken on a 64 bit kernel which will need to be fixed separately.

Fixes: CVE-2018-1118
Cc: stable@vger.kernel.org
Reported-by: Kevin Easton <kevin@guarana.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reported-by: syzbot+87cfa083e727a224754b@syzkaller.appspotmail.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 670ae9caaca467ea1bfd325cb2a5c98ba87f94ad)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 31bdfd296ced1f47b31f41ec948f5db49789bb0d..a922d3d28a20ea1b3cdc5815cfbf8dcbb81f24a1 100644 (file)
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2383,6 +2383,9 @@ struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
        struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
        if (!node)
                return NULL;
+
+       /* Make sure all padding within the structure is initialized. */
+       memset(&node->msg, 0, sizeof node->msg);
        node->vq = vq;
        node->msg.type = type;
        return node;