[PATCH] D144708: [clangd] Fix UB in scanPreamble

[Kadir Cetinkaya via Phabricator via cfe-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
kadircet marked an inline comment as done.
Closed by commit rGf393e1f6b3b4: [clangd] Fix UB in scanPreamble (authored by kadircet).

Changed prior to commit:
  https://reviews.llvm.org/D144708?vs=500101&id=500112#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D144708/new/

https://reviews.llvm.org/D144708

Files:
  clang-tools-extra/clangd/Preamble.cpp


Index: clang-tools-extra/clangd/Preamble.cpp
===================================================================
--- clang-tools-extra/clangd/Preamble.cpp
+++ clang-tools-extra/clangd/Preamble.cpp
@@ -332,6 +332,8 @@
   EmptyFS FS;
   // Build and run Preprocessor over the preamble.
   ParseInputs PI;
+  // Memory buffers below expect null-terminated && non-null strings. So make
+  // sure to always use PI.Contents!
   PI.Contents = Contents.str();
   PI.TFS = &FS;
   PI.CompileCommand = Cmd;
@@ -345,8 +347,8 @@
   // twice. However, it's important to precisely follow the preamble bounds used
   // elsewhere.
   auto Bounds = ComputePreambleBounds(*CI->getLangOpts(), *ContentsBuffer, 0);
-  auto PreambleContents =
-      llvm::MemoryBuffer::getMemBufferCopy(Contents.substr(0, Bounds.Size));
+  auto PreambleContents = llvm::MemoryBuffer::getMemBufferCopy(
+      llvm::StringRef(PI.Contents).take_front(Bounds.Size));
   auto Clang = prepareCompilerInstance(
       std::move(CI), nullptr, std::move(PreambleContents),
       // Provide an empty FS to prevent preprocessor from performing IO. This
@@ -739,9 +741,8 @@
   //   whole preamble, which is terribly slow.
   // - If scanning for Modified fails, cannot figure out newly added ones so
   //   there's nothing to do but generate an empty patch.
-  auto BaselineScan = scanPreamble(
-      // Contents needs to be null-terminated.
-      Baseline.Preamble.getContents(), Modified.CompileCommand);
+  auto BaselineScan =
+      scanPreamble(Baseline.Preamble.getContents(), Modified.CompileCommand);
   if (!BaselineScan) {
     elog("Failed to scan baseline of {0}: {1}", FileName,
          BaselineScan.takeError());


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D144708.500112.patch
Type: text/x-patch
Size: 1687 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20230224/3d0b39d1/attachment.bin>