Add an atexit handler to bypass calls into ERR_ string routines.

This works around Ubuntu's apparent lack of NO_ATEXIT support in their
build of OpenSSL.

src/libraries/Native/Unix/System.Security.Cryptography.Native/openssl.c

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#include "pal_err.h"
 #include "pal_types.h"
 #include "pal_utilities.h"
 #include "pal_safecrt.h"
@@ -1263,6 +1264,23 @@ static int32_t EnsureOpenSsl10Initialized()
     #define OPENSSL_INIT_NO_ATEXIT 0x00080000L
 #endif
 
+pthread_mutex_t g_err_mutex = PTHREAD_MUTEX_INITIALIZER;
+int volatile g_err_unloaded = 0;
+
+static void HandleShutdown()
+{
+    // Generally, a mutex to set a boolean is overkill, but this lock
+    // ensures that there are no callers already inside the string table
+    // when the unload (possibly) executes.
+    int result = pthread_mutex_lock(&g_err_mutex);
+    assert(!result && "Acquiring the error string table mutex failed.");
+
+    g_err_unloaded = 1;
+
+    result = pthread_mutex_unlock(&g_err_mutex);
+    assert(!result && "Releasing the error string table mutex failed.");
+}
+
 static int32_t EnsureOpenSsl11Initialized()
 {
     // In OpenSSL 1.0 we call OPENSSL_add_all_algorithms_conf() and ERR_load_crypto_strings(),
@@ -1279,6 +1297,10 @@ static int32_t EnsureOpenSsl11Initialized()
             OPENSSL_INIT_LOAD_SSL_STRINGS,
         NULL);
 
+    // As a fallback for when the NO_ATEXIT isn't respected, register a later
+    // atexit handler, so we will indicate that we're in the shutdown state
+    // and stop asking problematic questions from other threads.
+    atexit(HandleShutdown);
     return 0;
 }
 

src/libraries/Native/Unix/System.Security.Cryptography.Native/pal_err.c

@@ -34,10 +34,48 @@ uint64_t CryptoNative_ErrPeekLastError()
 
 const char* CryptoNative_ErrReasonErrorString(uint64_t error)
 {
-    return ERR_reason_error_string((unsigned long)error);
+    const char* errStr = NULL;
+
+#ifdef NEED_OPENSSL_1_1
+    int result = pthread_mutex_lock(&g_err_mutex);
+    assert(!result && "Acquiring the error string table mutex failed.");
+
+    if (!g_err_unloaded)
+    {
+#endif
+        errStr = ERR_reason_error_string((unsigned long)error);
+#ifdef NEED_OPENSSL_1_1
+    }
+
+    result = pthread_mutex_unlock(&g_err_mutex);
+    assert(!result && "Releasing the error string table mutex failed.");
+#endif
+
+    return errStr;
 }
 
 void CryptoNative_ErrErrorStringN(uint64_t e, char* buf, int32_t len)
 {
-    ERR_error_string_n((unsigned long)e, buf, Int32ToSizeT(len));
+#ifdef NEED_OPENSSL_1_1
+    int result = pthread_mutex_lock(&g_err_mutex);
+    assert(!result && "Acquiring the error string table mutex failed.");
+
+    if (!g_err_unloaded)
+    {
+#endif
+        ERR_error_string_n((unsigned long)e, buf, Int32ToSizeT(len));
+#ifdef NEED_OPENSSL_1_1
+    }
+    else
+    {
+        // If there's no string table, just make it be the empty string.
+        if (buf != NULL && len > 0)
+        {
+            buf[0] = 0;
+        }
+    }
+
+    result = pthread_mutex_unlock(&g_err_mutex);
+    assert(!result && "Releasing the error string table mutex failed.");
+#endif
 }

src/libraries/Native/Unix/System.Security.Cryptography.Native/pal_err.h

@@ -6,6 +6,13 @@
 #include <stdint.h>
 #include "opensslshim.h"
 
+#include <pthread.h>
+
+#ifdef NEED_OPENSSL_1_1
+extern pthread_mutex_t g_err_mutex;
+extern int volatile g_err_unloaded;
+#endif
+
 /*
 Shims the ERR_clear_error method.
 */