Re: [PATCH v2 1/2] vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console

Eric Biggers
2020-03-20T05:10:53Z

On Thu, Mar 19, 2020 at 08:36:28AM +0100, Jiri Slaby wrote:
> On 18. 03. 20, 23:38, Eric Biggers wrote:
> > --- a/drivers/tty/vt/vt.c
> > +++ b/drivers/tty/vt/vt.c
> > @@ -1102,6 +1102,9 @@ int vc_allocate(unsigned int currcons) /* return 0 on success */
> > tty_port_init(&vc->port);
> > INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
> >
> > + /* if this wasn't the case, we'd have to implement port->ops.destruct */
> > + BUILD_BUG_ON(offsetof(struct vc_data, port) != 0);
> > +
>
> This is 3 lines, implementing destruct would be like 4-5 :)? Please
> implement destruct instead.
>
> Otherwise looks good.
>

Actually implementing destruct would be 12 lines, see below. Remember there is
no tty_port_operations defined yet so we'd have to define it just for destruct.

Do you still prefer it?

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index ec34f1f5f3bb5..309a39197be0a 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1075,6 +1075,17 @@ static void visual_deinit(struct vc_data *vc)
module_put(vc->vc_sw->owner);
}

+static void vc_port_destruct(struct tty_port *port)
+{
+ struct vc_data *vc = container_of(port, struct vc_data, port);
+
+ kfree(vc);
+}
+
+static const struct tty_port_operations vc_port_ops = {
+ .destruct = vc_port_destruct,
+};
+
int vc_allocate(unsigned int currcons) /* return 0 on success */
{
struct vt_notifier_param param;
@@ -1100,11 +1111,9 @@ int vc_allocate(unsigned int currcons) /* return 0 on success */

vc_cons[currcons].d = vc;
tty_port_init(&vc->port);
+ vc->port.ops = &vc_port_ops;
INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);

- /* if this wasn't the case, we'd have to implement port->ops.destruct */
- BUILD_BUG_ON(offsetof(struct vc_data, port) != 0);
-
visual_init(vc, currcons, 1);

if (!*vc->vc_uni_pagedir_loc)