From 3548823b7c0ed8f985050d27d98c3f1145f0bea3 Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka@gmail.com>
Date: Thu, 13 Feb 2025 07:39:26 -0800
Subject: [PATCH] Revert "[libclang] Always Dup in createRef(StringRef)
 (#125020)"

This reverts commit e76739eeb952940b2979c70ba44a28fecf592695.
---
 clang/docs/ReleaseNotes.rst       |  3 ---
 clang/tools/libclang/CXString.cpp | 14 +++++++++++++-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e41ad384b84f7..03bddbe3e983a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -257,9 +257,6 @@ clang-format
 libclang
 --------
 
-- Fixed a buffer overflow in ``CXString`` implementation. The fix may result in
-  increased memory allocation.
-
 Code Completion
 ---------------
 
diff --git a/clang/tools/libclang/CXString.cpp b/clang/tools/libclang/CXString.cpp
index aaa8f8eeb67a1..5e427957a1092 100644
--- a/clang/tools/libclang/CXString.cpp
+++ b/clang/tools/libclang/CXString.cpp
@@ -87,7 +87,19 @@ CXString createRef(StringRef String) {
   if (String.empty())
     return createEmpty();
 
-  return createDup(String);
+  // If the string is not nul-terminated, we have to make a copy.
+
+  // FIXME: This is doing a one past end read, and should be removed! For memory
+  // we don't manage, the API string can become unterminated at any time outside
+  // our control.
+
+  if (String.data()[String.size()] != 0)
+    return createDup(String);
+
+  CXString Result;
+  Result.data = String.data();
+  Result.private_flags = (unsigned) CXS_Unmanaged;
+  return Result;
 }
 
 CXString createDup(StringRef String) {