From c000e9c1f409c926b766333c615c321eab82e366 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ivan=20Schre=CC=81ter?= <ivan.schreter@sap.com>
Date: Fri, 24 Feb 2023 21:51:46 +0100
Subject: [PATCH 1/2] Add NUL character at the end of copied error message

C++ error message returned by `what` must be NUL-terminated. However,
the current copy function only copied the characters, but didn't add
the NUL. Allocate one more byte and set it to NUL.
---
 src/cxx.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/cxx.cc b/src/cxx.cc
index 4958eb08b..d449429da 100644
--- a/src/cxx.cc
+++ b/src/cxx.cc
@@ -449,8 +449,9 @@ static_assert(!std::is_same<Vec<std::uint8_t>::const_iterator,
               "Vec<T>::const_iterator != Vec<T>::iterator");
 
 static const char *errorCopy(const char *ptr, std::size_t len) {
-  char *copy = new char[len];
+  char *copy = new char[len + 1];
   std::memcpy(copy, ptr, len);
+  copy[len] = 0;
   return copy;
 }
 

From eec29dc3a0f567fe40438c4f56f4f0a56349db88 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ivan=20Schre=CC=81ter?= <ivan.schreter@sap.com>
Date: Sun, 26 Feb 2023 17:21:49 +0100
Subject: [PATCH 2/2] Fix: Prevent crash on OOM in error copy

When the error message is copied, the allocation may fail. This would
terminate the process, since it's called from a `noexcept` function.

Make the allocation `nothrow` and handle `nullptr` in `what()` method
appropriately, returning a generic message saying that the message
cannot be allocated.

This also prevents a crash if `what()` is called on a moved object
(which is technically UB, but still better not to crash).
---
 src/cxx.cc | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/cxx.cc b/src/cxx.cc
index d449429da..c630647b7 100644
--- a/src/cxx.cc
+++ b/src/cxx.cc
@@ -448,10 +448,14 @@ static_assert(!std::is_same<Vec<std::uint8_t>::const_iterator,
                             Vec<std::uint8_t>::iterator>::value,
               "Vec<T>::const_iterator != Vec<T>::iterator");
 
-static const char *errorCopy(const char *ptr, std::size_t len) {
-  char *copy = new char[len + 1];
-  std::memcpy(copy, ptr, len);
-  copy[len] = 0;
+// Copy the error message into a private buffer and return it.
+// If the allocation fails, nullptr is returned.
+static const char *errorCopy(const char *ptr, std::size_t len) noexcept {
+  char *copy = new (std::nothrow) char[len + 1];
+  if (copy) {
+    std::memcpy(copy, ptr, len);
+    copy[len] = 0;
+  }
   return copy;
 }
 
@@ -497,7 +501,12 @@ Error &Error::operator=(Error &&other) &noexcept {
   return *this;
 }
 
-const char *Error::what() const noexcept { return this->msg; }
+const char *Error::what() const noexcept {
+  if (this->msg)
+    return this->msg;
+  else
+    return "<message not allocated>";
+}
 
 namespace {
 template <typename T>