Merge bitcoin/bitcoin#27930: util: Don't derive secure_allocator from std::allocator

07c59eda00841aafaafd8fd648217b56b1e907c9 Don't derive secure_allocator from std::allocator (Casey Carter)

Pull request description:

  Giving the C++ Standard Committee control of the public interface of your type means they will break it. C++23 adds a new `allocate_at_least` member to `std::allocator`. Very bad things happen when, say, `std::vector` uses `allocate_at_least` from `secure_allocator`'s base to allocate memory which it then tries to free with `secure_allocator::deallocate`.

  (Discovered by microsoft/STL#3712, which will be reverted by microsoft/STL#3819 before it ships.)

ACKs for top commit:
  jonatack:
    re-ACK 07c59eda00841aafaafd8fd648217b56b1e907c9 no change since my previous ACK apart from squashing the commits
  achow101:
    ACK 07c59eda00841aafaafd8fd648217b56b1e907c9
  john-moffett:
    ACK 07c59eda00841aafaafd8fd648217b56b1e907c9 Reviewed and tested. Performance appears unaffected in my environment.

Tree-SHA512: 23606c40414d325f5605a9244d4dd50907fdf5f2fbf70f336accb3a2cb98baa8acd2972f46eab1b7fdec1d28a843a96b06083cd2d09791cda7c90ee218e5bbd5

2 files changed, 39 insertions, 36 deletions

diff --git a/src/support/allocators/secure.h b/src/support/allocators/secure.h
index b2076bea07..558f835f11 100644
--- a/src/support/allocators/secure.h
+++ b/src/support/allocators/secure.h
@@ -17,27 +17,14 @@
 // out of memory and clears its contents before deletion.
 //
 template <typename T>
-struct secure_allocator : public std::allocator<T> {
-    using base = std::allocator<T>;
-    using traits = std::allocator_traits<base>;
-    using size_type = typename traits::size_type;
-    using difference_type = typename traits::difference_type;
-    using pointer = typename traits::pointer;
-    using const_pointer = typename traits::const_pointer;
-    using value_type = typename traits::value_type;
-    secure_allocator() noexcept {}
-    secure_allocator(const secure_allocator& a) noexcept : base(a) {}
+struct secure_allocator {
+    using value_type = T;
+
+    secure_allocator() = default;
     template <typename U>
-    secure_allocator(const secure_allocator<U>& a) noexcept : base(a)
-    {
-    }
-    ~secure_allocator() noexcept {}
-    template <typename Other>
-    struct rebind {
-        typedef secure_allocator<Other> other;
-    };
+    secure_allocator(const secure_allocator<U>&) noexcept {}
 
-    T* allocate(std::size_t n, const void* hint = nullptr)
+    T* allocate(std::size_t n)
     {
         T* allocation = static_cast<T*>(LockedPoolManager::Instance().alloc(sizeof(T) * n));
         if (!allocation) {
@@ -53,6 +40,17 @@ struct secure_allocator : public std::allocator<T> {
         }
         LockedPoolManager::Instance().free(p);
     }
+
+    template <typename U>
+    friend bool operator==(const secure_allocator&, const secure_allocator<U>&) noexcept
+    {
+        return true;
+    }
+    template <typename U>
+    friend bool operator!=(const secure_allocator&, const secure_allocator<U>&) noexcept
+    {
+        return false;
+    }
 };
 
 // This is exactly like std::string, but with a custom allocator.
diff --git a/src/support/allocators/zeroafterfree.h b/src/support/allocators/zeroafterfree.h
index 2dc644c242..6d50eb70a6 100644
--- a/src/support/allocators/zeroafterfree.h
+++ b/src/support/allocators/zeroafterfree.h
@@ -12,31 +12,36 @@
 #include <vector>
 
 template <typename T>
-struct zero_after_free_allocator : public std::allocator<T> {
-    using base = std::allocator<T>;
-    using traits = std::allocator_traits<base>;
-    using size_type = typename traits::size_type;
-    using difference_type = typename traits::difference_type;
-    using pointer = typename traits::pointer;
-    using const_pointer = typename traits::const_pointer;
-    using value_type = typename traits::value_type;
-    zero_after_free_allocator() noexcept {}
-    zero_after_free_allocator(const zero_after_free_allocator& a) noexcept : base(a) {}
+struct zero_after_free_allocator {
+    using value_type = T;
+
+    zero_after_free_allocator() noexcept = default;
     template <typename U>
-    zero_after_free_allocator(const zero_after_free_allocator<U>& a) noexcept : base(a)
+    zero_after_free_allocator(const zero_after_free_allocator<U>&) noexcept
+    {
+    }
+
+    T* allocate(std::size_t n)
     {
+        return std::allocator<T>{}.allocate(n);
     }
-    ~zero_after_free_allocator() noexcept {}
-    template <typename Other>
-    struct rebind {
-        typedef zero_after_free_allocator<Other> other;
-    };
 
     void deallocate(T* p, std::size_t n)
     {
         if (p != nullptr)
             memory_cleanse(p, sizeof(T) * n);
-        std::allocator<T>::deallocate(p, n);
+        std::allocator<T>{}.deallocate(p, n);
+    }
+
+    template <typename U>
+    friend bool operator==(const zero_after_free_allocator&, const zero_after_free_allocator<U>&) noexcept
+    {
+        return true;
+    }
+    template <typename U>
+    friend bool operator!=(const zero_after_free_allocator&, const zero_after_free_allocator<U>&) noexcept
+    {
+        return false;
     }
 };