From 4678e44bb28c00dc22771a0ef2684a4d46715ab0 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Fri, 29 May 2020 23:39:39 +0200
Subject: [PATCH] src: perform bounds checking on error source line

Fixes: https://github.com/nodejs/node/issues/33578

PR-URL: https://github.com/nodejs/node/pull/33645
Reviewed-By: Rich Trott <rtrott@gmail.com>
---
 src/node_errors.cc | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/node_errors.cc b/src/node_errors.cc
index 4f8b003d8da225..3f0bb68a2974c7 100644
--- a/src/node_errors.cc
+++ b/src/node_errors.cc
@@ -55,6 +55,7 @@ static std::string GetErrorSource(Isolate* isolate,
   MaybeLocal<String> source_line_maybe = message->GetSourceLine(context);
   node::Utf8Value encoded_source(isolate, source_line_maybe.ToLocalChecked());
   std::string sourceline(*encoded_source, encoded_source.length());
+  *added_exception_line = false;
 
   // If source maps have been enabled, the exception line will instead be
   // added in the JavaScript context:
@@ -62,12 +63,10 @@ static std::string GetErrorSource(Isolate* isolate,
   const bool has_source_map_url =
       !message->GetScriptOrigin().SourceMapUrl().IsEmpty();
   if (has_source_map_url && env->source_maps_enabled()) {
-    *added_exception_line = false;
     return sourceline;
   }
 
   if (sourceline.find("node-do-not-add-exception-line") != std::string::npos) {
-    *added_exception_line = false;
     return sourceline;
   }
 
@@ -114,6 +113,13 @@ static std::string GetErrorSource(Isolate* isolate,
                             linenum,
                             sourceline.c_str());
   CHECK_GT(buf.size(), 0);
+  *added_exception_line = true;
+
+  if (start > end ||
+      start < 0 ||
+      static_cast<size_t>(end) > sourceline.size()) {
+    return buf;
+  }
 
   constexpr int kUnderlineBufsize = 1020;
   char underline_buf[kUnderlineBufsize + 4];
@@ -136,7 +142,6 @@ static std::string GetErrorSource(Isolate* isolate,
   CHECK_LE(off, kUnderlineBufsize);
   underline_buf[off++] = '\n';
 
-  *added_exception_line = true;
   return buf + std::string(underline_buf, off);
 }