[TCP]: sysctl to allow TCP window > 32767 sans wscale

Back in the dark ages, we had to be conservative and only allow 15-bit
window fields if the window scale option was not negotiated.  Some
ancient stacks used a signed 16-bit quantity for the window field of
the TCP header and would get confused.

Those days are long gone, so we can use the full 16-bits by default
now.

There is a sysctl added so that we can still interact with such old
stacks

Signed-off-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 651298ba019a..f12007b80a46 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -355,6 +355,13 @@ somaxconn - INTEGER
         Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
         for TCP sockets.
 
+tcp_workaround_signed_windows - BOOLEAN
+        If set, assume no receipt of a window scaling option means the
+        remote TCP is broken and treats the window as a signed quantity.
+        If unset, assume the remote TCP is not broken even if we do
+        not receive a window scaling option from them.
+        Default: 0
+
 IP Variables:
 
 ip_local_port_range - 2 INTEGERS