netdev - Re: [PATCH net-next] net: Fail explicit bind to local reserved ports

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Message-Id: <20190830.142202.1082989152863915040.davem@davemloft.net>
Date:   Fri, 30 Aug 2019 14:22:02 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     subashab@...eaurora.org
Cc:     netdev@...r.kernel.org, stranche@...eaurora.org
Subject: Re: [PATCH net-next] net: Fail explicit bind to local reserved
 ports

From: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Date: Wed, 28 Aug 2019 21:26:54 -0600

> Reserved ports may have some special use cases which are not suitable
> for use by general userspace applications. Currently, ports specified
> in ip_local_reserved_ports will not be returned only in case of
> automatic port assignment.
> 
> In some cases, it maybe required to prevent the host from assigning
> the ports even in case of explicit binds. Consider the case of a
> transparent proxy where packets are being redirected. In case a socket
> matches this connection, packets from this application would be
> incorrectly sent to one of the endpoints.
> 
> Add a boolean sysctl flag 'reserved_port_bind'. Default value is 1
> which preserves the existing behavior. Setting the value to 0 will
> prevent userspace applications from binding to these ports even when
> they are explicitly requested.
> 
> Cc: Sean Tranchetti <stranche@...eaurora.org>
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>

I don't know how happy I am about this.  Whatever sets up the transparent
proxy business can block any attempt to communicate over these ports.

Also, protocols like SCTP need the new handling too.