Merge pull request #1244 from microsoft/bugfix-inetstack-window-scale

[inetstack] Bug Fix: Clamp window scale to 14

Author: ppenna

src/rust/inetstack/protocols/tcp/active_open.rs

@@ -18,7 +18,10 @@ use crate::{
         ip::IpProtocol,
         ipv4::Ipv4Header,
         tcp::{
-            constants::FALLBACK_MSS,
+            constants::{
+                FALLBACK_MSS,
+                MAX_WINDOW_SCALE,
+            },
             established::{
                 congestion_control::{
                     self,
@@ -180,14 +183,25 @@ impl<N: NetworkRuntime> SharedActiveOpenSocket<N> {
             }
         }
 
-        let (local_window_scale, remote_window_scale) = match remote_window_scale {
-            Some(w) => (self.tcp_config.get_window_scale() as u32, w),
+        let (local_window_scale, remote_window_scale): (u32, u8) = match remote_window_scale {
+            Some(remote_window_scale) => {
+                let local: u32 = if self.tcp_config.get_window_scale() > 14 {
+                    warn!("local windows scale larger than 14 is incorrect, so setting to 14. See RFC 1323.");
+                    MAX_WINDOW_SCALE as u32
+                } else {
+                    self.tcp_config.get_window_scale() as u32
+                };
+                let remote: u8 = if remote_window_scale > 14 {
+                    warn!("remote windows scale larger than 14 is incorrect, so setting to 14. See RFC 1323.");
+                    MAX_WINDOW_SCALE as u8
+                } else {
+                    remote_window_scale
+                };
+                (local, remote)
+            },
             None => (0, 0),
         };
 
-        // TODO(RFC1323): Clamp the scale to 14 instead of panicking.
-        assert!(local_window_scale <= 14 && remote_window_scale <= 14);
-
         let rx_window_size: u32 = expect_ok!(
             expect_some!(
                 (self.tcp_config.get_receive_window_size() as u32).checked_shl(local_window_scale as u32),

src/rust/inetstack/protocols/tcp/constants.rs

@@ -5,5 +5,6 @@ pub use crate::runtime::network::consts::{
     DEFAULT_MSS,
     FALLBACK_MSS,
     MAX_MSS,
+    MAX_WINDOW_SCALE,
     MIN_MSS,
 };

src/rust/runtime/network/consts.rs

@@ -36,3 +36,7 @@ pub const DEFAULT_MSS: usize = 1450;
 ///
 /// TODO: This Should be Generic
 pub const RECEIVE_BATCH_SIZE: usize = 4;
+
+/// Maximum local and remote window scaling factor.
+/// See: RFC 1323, Section 2.3.
+pub const MAX_WINDOW_SCALE: usize = 14;