[PATCH 0/2] SUNRPC: Clean up port reuse behavior on reconnects

[Vallish Vaidyeshwara <vallish@amazon.com>]

We have seen examples of NFSv4 client reconnections failing due to
client source port reuse combined with stateful TCP state tracking in
middleboxes.

Commit 0f7a622ca616 ("rpc: xs_bind - do not bind when requesting a
random ephemeral port"), commit 4dda9c8a5e34 ("SUNRPC: Set SO_REUSEPORT
socket option for TCP connections"), and commit 1f4c17a03ba7 ("SUNRPC:
Handle EADDRNOTAVAIL on connection failures") had unintended side effects
of making port reuse dependent on whether that client uses reserved or
non-reserved source ports.

This series fixes the observed NFSv4 client reconnect failures by
choosing a new source port regardless of which port range is in use
for RST or FIN terminating the prior connection. This series does
not restore the original always-reuse behavior that existed prior to
commits mentioned above.

Patch 1:
--------
SUNRPC: Need to reuse non-reserved port for reconnect

This patch restores the original behavior of port reuse in all
scenarios.

Patch 2:
--------
SUNRPC: Reconnect with new port on server initiated connection
    termination

Client uses a new port only in cases where server has terminated
the connection explicitly using RST or FIN.

Proposed outcome with this patch series:
----------------------------------------
------------------------------------------------------------------
| Port type | Connection termination | Current    | With this    |
|           |         type           | behavior   | patch series |
------------------------------------------------------------------
|  Reserved | Network partition-DROP | Reuse port | Reuse port   |
------------------------------------------------------------------
|  Reserved | FIN from server        | Reuse port | New port     |
------------------------------------------------------------------
|  Reserved | RST from server        | Reuse port | New port     |
------------------------------------------------------------------
|  Non-Resv | Network partition-DROP | New port   | Reuse port   |
------------------------------------------------------------------
|  Non-Resv | FIN from server        | New port   | New port     |
------------------------------------------------------------------
|  Non-Resv | RST from server        | New port   | New port     |
------------------------------------------------------------------

 net/sunrpc/xprtsock.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

-- 
2.7.3.AMZN