From: Maciej Żenczykowski <redacted>
Date: Wed, 27 Nov 2019 12:50:39 -0800

On Wed, Nov 27, 2019 at 5:14 AM Marcelo Ricardo Leitner
[off-list ref] wrote:

quoted

On Tue, Nov 26, 2019 at 04:13:13PM -0800, Maciej Żenczykowski wrote:

quoted

From: Maciej Żenczykowski <redacted>

and associated inet_is_local_unbindable_port() helper function:
use it to make explicitly binding to an unbindable port return
-EPERM 'Operation not permitted'.

Autobind doesn't honour this new sysctl since:
  (a) you can simply set both if that's the behaviour you desire
  (b) there could be a use for preventing explicit while allowing auto
  (c) it's faster in the relatively critical path of doing port selection
      during connect() to only check one bitmap instead of both

...

quoted

If we *know* that certain ports are simply unusable, then it's better
nothing even gets the opportunity to try to use them.  This way we at
least get a quick failure, instead of some sort of timeout (or possibly
even corruption of the data stream of the non-kernel based use case).

This is doable with SELinux today, no?

Perhaps, but SELinux isn't used by many distros, including the servers
where I have nics that steal some ports.  It's also much much
more difficult, requiring a policy, compilers, etc... and it gets even
more complex if you need to dynamically modify the set of ports,
which requires extra tools and runtime permissions.

I can see both sides of this argument, but anyways this is a new features and
thus net-next material.  It's nice to keep this discussion going, of course,
but if this trends in the positive you still need to resubmit this when
net-next opens back up.

Thanks.