[clang] [clang-format] Fix crash in TokenAnnotator (PR #82349)

[Emilia Kond via cfe-commits]

https://github.com/rymiel created https://github.com/llvm/llvm-project/pull/82349

The while loop on line 3814 can cause a segmentation fault getting the Next field on a nullptr. This is because further down, on line 3823, there is another for loop, which assigns Tok to Tok->Next in its initializer. This for loop has a condition to check if the result of that isn't null. If it is, the loop is skipped and we drop back out to the outer loop, except, now Tok is null, and we try to dereference it without checking first.

This patch adds a defensive check that returns if Tok->Next is null before we make it to the second for loop.

Fixes https://github.com/llvm/llvm-project/issues/82328

>From 25ca98534f0d5dbd96ff74c802528171787ced45 Mon Sep 17 00:00:00 2001
From: Emilia Kond <emilia at rymiel.space>
Date: Tue, 20 Feb 2024 14:11:33 +0200
Subject: [PATCH] [clang-format] Fix crash in TokenAnnotator

The while loop on line 3814 can cause a segmentation fault getting the
Next field on a nullptr. This is because further down, on line 3823,
there is another for loop, which assigns Tok to Tok->Next in its
initializer. This for loop has a condition to check if the result of that
isn't null. If it is, the loop is skipped and we drop back out to the
outer loop, except, now Tok is null, and we try to dereference it without
checking first.

This patch adds a defensive check that returns if Tok->Next is null
before we make it to the second for loop.

Fixes https://github.com/llvm/llvm-project/issues/82328
---
 clang/lib/Format/TokenAnnotator.cpp   | 2 +-
 clang/unittests/Format/FormatTest.cpp | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index ec7b7f4dbe3470..a38ba8762f8505 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -3817,7 +3817,7 @@ void TokenAnnotator::calculateFormattingInformation(AnnotatedLine &Line) const {
         do {
           Tok = Tok->Next;
         } while (Tok && Tok->isNot(TT_OverloadedOperatorLParen));
-        if (!Tok)
+        if (!Tok || !Tok->Next)
           break;
         const auto *LeftParen = Tok;
         for (Tok = Tok->Next; Tok && Tok != LeftParen->MatchingParen;
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 24f62af8ddcb87..3a3c88f609af7a 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -13503,6 +13503,9 @@ TEST_F(FormatTest, IncorrectCodeUnbalancedBraces) {
   verifyFormat("{");
   verifyFormat("#})");
   verifyNoCrash("(/**/[:!] ?[).");
+  verifyNoCrash("struct X{"
+                "  operator iunt("
+                "};");
 }
 
 TEST_F(FormatTest, IncorrectUnbalancedBracesInMacrosWithUnicode) {