Re: [PATCH stable v4.19.99]: net: hv_sock: Remove the accept port restriction

[Sasha Levin <sashal@kernel.org>]

On Fri, Jan 24, 2020 at 03:08:18AM +0000, Sunil Muthuswamy wrote:
>commit c742c59e1fbd ("hv_sock: Remove the accept port restriction")
>
>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@microsoft.com>
>Signed-off-by: David S. Miller <davem@davemloft.net>

I'll queue it up when the current release is out in a day or so, thanks!

-- 
Thanks,
Sasha