Fix DhParams copy-assignment and copy-constructor

DhParams copy-assignement was implemented as non-op operator.
This is weird for a copy to do nothing!
No intends are indicated to help.
Seems only done to help MSVC compiler, but this is WRONG
and cause a SECURITY FAILURE as the DhParam is not set
as supposed to be.
Consequence observed on UWP daemon: the anonymous connection
cannot be done and the certificate is always send in cleartext.

The fix consists in using the dedicated gnutls API
to copy correctly the internal dh_params C structure.
This is used to implement copy-assignement and copy-constructor
methods

Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>
Change-Id: I49d3a3fd2c0a2ed5fde0bd251efbad589c830c70

src/security/tls_session.cpp

@@ -82,6 +82,25 @@ DhParams::DhParams(const std::vector<uint8_t>& data)
             throw std::runtime_error(std::string("Error importing DH params: ") + gnutls_strerror(ret_pem) + " " + gnutls_strerror(ret_der));
 }
 
+DhParams&
+DhParams::operator=(const DhParams& other)
+{
+    if (not params_) {
+        // We need a valid DH params pointer for the copy
+        gnutls_dh_params_t new_params_;
+        auto err = gnutls_dh_params_init(&new_params_);
+        if (err != GNUTLS_E_SUCCESS)
+            throw std::runtime_error(std::string("Error initializing DH params: ") + gnutls_strerror(err));
+        params_.reset(new_params_);
+    }
+
+    auto err = gnutls_dh_params_cpy(params_.get(), other.get());
+    if (err != GNUTLS_E_SUCCESS)
+        throw std::runtime_error(std::string("Error copying DH params: ") + gnutls_strerror(err));
+
+    return *this;
+}
+
 std::vector<uint8_t>
 DhParams::serialize() const
 {

src/security/tls_session.h

@@ -22,6 +22,7 @@
 #pragma once
 
 #include "threadloop.h"
+#include "noncopyable.h"
 
 #include <gnutls/gnutls.h>
 #include <gnutls/dtls.h>
@@ -41,6 +42,7 @@
 #include <atomic>
 #include <iterator>
 #include <array>
+#include <stdexcept>
 
 namespace ring {
 class IceTransport;
@@ -71,13 +73,18 @@ class DhParams {
 public:
     DhParams() = default;
     DhParams(DhParams&&) = default;
-
-    DhParams& operator =(const DhParams& other){
-        return *this;
+    DhParams(const DhParams& other) {
+        *this = other;
     }
 
-    /** Take ownership of gnutls_dh_params */
-    explicit DhParams(gnutls_dh_params_t p) : params_(p, gnutls_dh_params_deinit) {};
+    DhParams& operator=(DhParams&& other) = default;
+    DhParams& operator=(const DhParams& other);
+
+    /// \brief Construct by taking ownership of given gnutls DH params
+    ///
+    /// User should not call gnutls_dh_params_deinit on given \a raw_params.
+    /// The object is stolen and its live is manager by our object.
+    explicit DhParams(gnutls_dh_params_t p) : params_ {p, gnutls_dh_params_deinit} {}
 
     /** Deserialize DER or PEM encoded DH-params */
     DhParams(const std::vector<uint8_t>& data);
@@ -99,7 +106,7 @@ public:
     static DhParams generate();
 
 private:
-    std::unique_ptr<gnutls_dh_params_int, decltype(gnutls_dh_params_deinit)&> params_ {nullptr, gnutls_dh_params_deinit};
+    std::unique_ptr<gnutls_dh_params_int, decltype(gnutls_dh_params_deinit)*> params_ {nullptr, gnutls_dh_params_deinit};
 };
 
 struct TlsParams {