Subject: Re: [PATCH v7 0/4] Support administratively closing application sockets

From: Stephen Hemminger <[email-masked]>
Date: Wed, 16 Dec 2015 07:43:34 -0800

On Wed, 16 Dec 2015 12:30:01 +0900
Lorenzo Colitti <[email-masked]> wrote:

> This patchset adds the ability to administratively close a socket
> without any action from the process owning the socket or the
> socket protocol.
> 
> It implements this by adding a new diag_destroy function pointer
> to struct proto. In-kernel callers can access this functionality
> directly by calling sk->sk_prot->diag_destroy(sk, err).
> 
> It also exposes this functionality to userspace via a new
> SOCK_DESTROY operation in the NETLINK_SOCK_DIAG sockets. This
> allows a privileged userspace process, such as a connection
> manager or system administration tool, to close sockets belonging
> to other apps when the network they were established on has
> disconnected. It is needed on laptops and mobile hosts to ensure
> that network switches / disconnects do not result in applications
> being blocked for long periods of time (minutes) in read or
> connect calls on TCP sockets that will never succeed because the
> IP address they are bound to is no longer on the system. Closing
> the sockets causes these calls to fail fast and allows the apps
> to reconnect on another network.
> 
> Userspace intervention is necessary because in many cases the
> kernel does not have enough information to know that a connection
> is now inoperable. The kernel can know if a packet can't be
> routed, but in general it won't know if a TCP connection is stuck
> because it is now routed to a network where its source address is
> no longer valid [5][6].

I see no security checks in the diag infrastructure.
Up until now diag has been read-only access and therefore has been
allowed for all users.