From 27c7054505ebf659319bea12892e7190e01b70c6 Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Tue, 21 Dec 2021 10:47:55 +1100
Subject: [PATCH] [client] x11: protect against msc overflow with jitRender

---
 client/displayservers/X11/x11.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/client/displayservers/X11/x11.c b/client/displayservers/X11/x11.c
index 7de18334..956a2db5 100644
--- a/client/displayservers/X11/x11.c
+++ b/client/displayservers/X11/x11.c
@@ -117,7 +117,16 @@ static void x11DoPresent(uint64_t msc)
 
   uint64_t refill;
   if (!first)
-    refill = 50 - (lastMsc - msc);
+  {
+    const uint64_t delta = (lastMsc >= msc) ?
+      lastMsc - msc :
+      ~0ULL - msc + lastMsc;
+
+    if (delta > 50)
+      return;
+
+    refill = 50 - delta;
+  }
   else
   {
     refill  = 50;