linux-kernel - Re: [PATCH net]: hv_sock: Remove the accept port restriction

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Date:   Tue, 14 Jan 2020 11:51:27 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     sunilmut@...rosoft.com
Cc:     netdev@...r.kernel.org, decui@...rosoft.com,
        sthemmin@...rosoft.com, sashal@...nel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net]: hv_sock: Remove the accept port restriction

From: Sunil Muthuswamy <sunilmut@...rosoft.com>
Date: Tue, 14 Jan 2020 00:52:14 +0000

> Currently, hv_sock restricts the port the guest socket can accept
> connections on. hv_sock divides the socket port namespace into two parts
> for server side (listening socket), 0-0x7FFFFFFF & 0x80000000-0xFFFFFFFF
> (there are no restrictions on client port namespace). The first part
> (0-0x7FFFFFFF) is reserved for sockets where connections can be accepted.
> The second part (0x80000000-0xFFFFFFFF) is reserved for allocating ports
> for the peer (host) socket, once a connection is accepted.
> This reservation of the port namespace is specific to hv_sock and not
> known by the generic vsock library (ex: af_vsock). This is problematic
> because auto-binds/ephemeral ports are handled by the generic vsock
> library and it has no knowledge of this port reservation and could
> allocate a port that is not compatible with hv_sock (and legitimately so).
> The issue hasn't surfaced so far because the auto-bind code of vsock
> (__vsock_bind_stream) prior to the change 'VSOCK: bind to random port for
> VMADDR_PORT_ANY' would start walking up from LAST_RESERVED_PORT (1023) and
> start assigning ports. That will take a large number of iterations to hit
> 0x7FFFFFFF. But, after the above change to randomize port selection, the
> issue has started coming up more frequently.
> There has really been no good reason to have this port reservation logic
> in hv_sock from the get go. Reserving a local port for peer ports is not
> how things are handled generally. Peer ports should reflect the peer port.
> This fixes the issue by lifting the port reservation, and also returns the
> right peer port. Since the code converts the GUID to the peer port (by
> using the first 4 bytes), there is a possibility of conflicts, but that
> seems like a reasonable risk to take, given this is limited to vsock and
> that only applies to all local sockets.
> 
> Signed-off-by: Sunil Muthuswamy <sunilmut@...rosoft.com>

Applied.