From b1571febfdc41a8ae84ea49e55cec0ee141d272b Mon Sep 17 00:00:00 2001
From: Herman Semenoff <GermanAizek@yandex.ru>
Date: Sun, 30 Aug 2026 01:10:31 +0300
Subject: [PATCH] fb: Avoid potential out-of-bounds shift amounts in fbBlt

In fbBlt(), explicitly check (srcX < dstX) in the alternate shift calculation
branch so that shift values (leftShift and rightShift) remain strictly within
valid bit-width bounds [0..FB_UNIT - 1], avoiding potential 32-bit shift
undefined behavior warnings
---
 fb/fbblt.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fb/fbblt.c b/fb/fbblt.c
index e7b06c283..bb0183aca 100644
--- a/fb/fbblt.c
+++ b/fb/fbblt.c
@@ -222,10 +222,14 @@ fbBlt(FbBits * srcLine,
             leftShift = srcX - dstX;
             rightShift = FB_UNIT - leftShift;
         }
-        else {
+        else if (srcX < dstX) {
             rightShift = dstX - srcX;
             leftShift = FB_UNIT - rightShift;
         }
+        else {
+            leftShift = 0;
+            rightShift = 0;
+        }
         while (height--) {
             src = srcLine;
             srcLine += srcStride;