Re: [PATCH -mm 7/7] forbid the use of the unshare syscall on ipc namespaces

[Cedric Le Goater <clg@fr.ibm.com>]

Kirill Korotaev wrote:

> This patch looks as an overkill for me.

it's a standalone patch. It can be dropped. I think there is some value to
it as we already agree

> If you really care about things you describe, you can forbid unsharing
> in cases:
> 
> 1.
>        undo_list = tsk->sysvsem.undo_list;
>        if (undo_list)
>                REFUSE_UNSHARE;
> 2. vma exists with vma->vm_ops == &shm_vm_ops;
> 3. file opened with f_op == &shm_file_operations

and there are also the netlink sockets mq_notify.

OK, so we agree that ipc namespaces cannot be unshared without extra
checks. I like the firewall approach : it's not safe, don't allow it. Which
is what the patch is doing : we can't unshare ipc namespace safely so let's
just forbid it :

	if (unshare_flags & CLONE_NEWIPC)
		goto bad_unshare_out;

simple, nop ? :)

> I also dislike exec() operation for such sort of things since you can
> have no executable at hands due to changed fs namespace.

what do you mean ? fs namespace doesn't change bc you need it to load the
new process image/interpreter.

C.