[clang] [clang] Fix null buffer dereference in InitializeFileRemapping (PR #201289)

[Krisitan Erik Olsen via cfe-commits]

https://github.com/Kristianerik updated https://github.com/llvm/llvm-project/pull/201289

>From 10a3cc532415078c19e809396bad1c457f97336a Mon Sep 17 00:00:00 2001
From: Kristianerik <46120297+Kristianerik at users.noreply.github.com>
Date: Wed, 3 Jun 2026 01:06:38 -0700
Subject: [PATCH 1/2] [clang] Fix null buffer dereference in
 InitializeFileRemappingWhen a module compilation fails partway through, a
 null buffer entrycan be left in PreprocessorOptions::RemappedFileBuffers. The
 existingcode in InitializeFileRemapping unconditionally dereferences
 RB.secondvia getBufferSize() and getMemBufferRef(), causing a crash.Add a
 null check consistent with the existing pattern in theRemappedFiles loop
 below, which already checks for missing filesbefore use.Fixes:
 https://github.com/llvm/llvm-project/issues/201188

---
 clang/lib/Frontend/CompilerInstance.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 9e88abbece7f2..92a116af066a8 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -413,6 +413,13 @@ static void InitializeFileRemapping(DiagnosticsEngine &Diags,
                                     const PreprocessorOptions &InitOpts) {
   // Remap files in the source manager (with buffers).
   for (const auto &RB : InitOpts.RemappedFileBuffers) {
+    // Skip entries with a null buffer — this can occur when a module
+    // compilation fails partway through, leaving an uninitialized entry
+    // in RemappedFileBuffers. Treat it as a missing file and continue.
+    if (!RB.second) {
+      Diags.Report(diag::err_fe_remap_missing_to_file) << RB.first << "(null buffer)";
+      continue;
+    }
     // Create the file entry for the file that we're mapping from.
     FileEntryRef FromFile =
         FileMgr.getVirtualFileRef(RB.first, RB.second->getBufferSize(), 0);

>From 9bf6d1978229b284e402d22f144c69365ae40a11 Mon Sep 17 00:00:00 2001
From: Kristianerik <46120297+Kristianerik at users.noreply.github.com>
Date: Wed, 3 Jun 2026 01:49:47 -0700
Subject: [PATCH 2/2] [clang] clang-format: wrap long line in
 InitializeFileRemapping

---
 clang/lib/Frontend/CompilerInstance.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 92a116af066a8..d9d02cb21a8f2 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -417,7 +417,8 @@ static void InitializeFileRemapping(DiagnosticsEngine &Diags,
     // compilation fails partway through, leaving an uninitialized entry
     // in RemappedFileBuffers. Treat it as a missing file and continue.
     if (!RB.second) {
-      Diags.Report(diag::err_fe_remap_missing_to_file) << RB.first << "(null buffer)";
+      Diags.Report(diag::err_fe_remap_missing_to_file)
+          << RB.first << "(null buffer)";
       continue;
     }
     // Create the file entry for the file that we're mapping from.