[PATCH v2 2/2] MdeModulePkg/Tcp4Dxe: Add wnd scale check before shrinking window

["atepin@kraftway.ru" <atepin@kraftway.ru>]

Moving Right window edge to the left on sender side without additional
check can lead to the TCP deadlock, when receiver ACKs proper segment,
while sender discards it for future ACK. To prevent this add check if
usable window (or shrink amount in this case) is bigger then receiver's
window scale factor.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Andrey Tepin <atepin@kraftway.ru>
---
 MdeModulePkg/Universal/Network/Tcp4Dxe/Tcp4Input.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/MdeModulePkg/Universal/Network/Tcp4Dxe/Tcp4Input.c b/MdeModulePkg/Universal/Network/Tcp4Dxe/Tcp4Input.c
index 1000538..77110d8 100644
--- a/MdeModulePkg/Universal/Network/Tcp4Dxe/Tcp4Input.c
+++ b/MdeModulePkg/Universal/Network/Tcp4Dxe/Tcp4Input.c
@@ -1187,8 +1187,21 @@ TcpInput (
       }
 
       if (TCP_SEQ_LT (Right, Tcb->SndNxt)) {
+        DEBUG (
+          (EFI_D_WARN,
+          "TcpInput: peer advise negative useable window for connected TCB %p\n",
+          Tcb)
+          );
 
-        Tcb->SndNxt = Right;
+        INT32 Usable = Tcb->SndNxt - Right;
+        if ((Usable >> Tcb->SndWndScale) > 0) {
+          DEBUG (
+            (EFI_D_WARN,
+            "TcpInput: SndNxt is out of window by more than window scale for TCB %p\n",
+            Tcb)
+            );
+          Tcb->SndNxt = Right;
+        }
 
         if (Right == Tcb->SndUna) {
 
-- 
2.7.4