Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup

[Linus Torvalds]

On Fri, Apr 8, 2016 at 11:51 AM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
>
> Given that concern under the rule we don't break userspace we have to
> check the permissions of /dev/pts/ptmx when we are creating a new pty,
> on a instance of devpts that was created with newinstance.

The rule is that we don't break existing installations.

If somebody has root and installs a "ptmx" node in an existing mount
space next to a pts subdirectory, that's not a security issue, nor is
it going to break any existing installation.

The whole point of the patch is that yes, we change semantics. A
change of semantics means that people will see situations where the
behavior is different. But that's not "breaking user space", that's
just "ok, you can see a difference".

                Linus