netdev - Re: [PATCH] net: introduce ip_local_unbindable

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Message-ID: <20191127131407.GA377783@localhost.localdomain>
Date:   Wed, 27 Nov 2019 10:14:07 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Maciej Żenczykowski <zenczykowski@...il.com>
Cc:     Maciej Żenczykowski <maze@...gle.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Sean Tranchetti <stranche@...eaurora.org>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Linux SCTP <linux-sctp@...r.kernel.org>
Subject: Re: [PATCH] net: introduce ip_local_unbindable_ports sysctl

On Tue, Nov 26, 2019 at 04:13:13PM -0800, Maciej Żenczykowski wrote:
> From: Maciej Żenczykowski <maze@...gle.com>
> 
> 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
...
> 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?