ENGINE's init() and finish() handler functions are used when the ENGINE is

being enabled or disabled (respectively) for operation. Additionally, each
ENGINE has a constructor function where it can do more 'structural' level
intialisations such as loading error strings, creating "ex_data" indices,
etc. This change introduces a handler function that gives an ENGINE a
corresponding opportunity to cleanup when the ENGINE is being destroyed. It
also adds the "get/set" API functions that control this "destroy" handler
function in an ENGINE.

crypto/engine/engine.h

@@ -371,6 +371,7 @@ int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth);
 int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth);
 int ENGINE_set_BN_mod_exp(ENGINE *e, BN_MOD_EXP bn_mod_exp);
 int ENGINE_set_BN_mod_exp_crt(ENGINE *e, BN_MOD_EXP_CRT bn_mod_exp_crt);
+int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f);
 int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f);
 int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f);
 int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f);
@@ -409,6 +410,7 @@ int ENGINE_cipher_num(const ENGINE *e);
 const EVP_CIPHER *ENGINE_get_cipher(const ENGINE *e, int n);
 BN_MOD_EXP ENGINE_get_BN_mod_exp(const ENGINE *e);
 BN_MOD_EXP_CRT ENGINE_get_BN_mod_exp_crt(const ENGINE *e);
+ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e);
 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e);
 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e);
 ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e);

crypto/engine/engine_int.h

@@ -112,6 +112,7 @@ struct engine_st
 
 	BN_MOD_EXP bn_mod_exp;
 	BN_MOD_EXP_CRT bn_mod_exp_crt;
+	ENGINE_GEN_INT_FUNC_PTR	destroy;
 	ENGINE_GEN_INT_FUNC_PTR init;
 	ENGINE_GEN_INT_FUNC_PTR finish;
 	ENGINE_CTRL_FUNC_PTR ctrl;

crypto/engine/engine_list.c

@@ -415,6 +415,10 @@ static int ENGINE_free_util(ENGINE *e, int locked)
 		abort();
 		}
 #endif
+	/* Give the ENGINE a chance to do any structural cleanup corresponding
+	 * to allocation it did in its constructor (eg. unload error strings) */
+	if(e->destroy)
+		e->destroy(e);
 	sk_ENGINE_EVP_CIPHER_pop_free(e->ciphers,ENGINE_free_engine_cipher);
 	CRYPTO_free_ex_data(CRYPTO_EX_INDEX_ENGINE, e, &e->ex_data);
 	OPENSSL_free(e);
@@ -532,6 +536,12 @@ int ENGINE_set_BN_mod_exp_crt(ENGINE *e, BN_MOD_EXP_CRT bn_mod_exp_crt)
 	return 1;
 	}
 
+int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f)
+	{
+	e->destroy = destroy_f;
+	return 1;
+	}
+
 int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f)
 	{
 	e->init = init_f;
@@ -648,6 +658,11 @@ BN_MOD_EXP_CRT ENGINE_get_BN_mod_exp_crt(const ENGINE *e)
 	return e->bn_mod_exp_crt;
 	}
 
+ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e)
+	{
+	return e->destroy;
+	}
+
 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e)
 	{
 	return e->init;