Fixing a crash after applying the wrong TLS configuration.

When an invalid TLS configuration is applied (such as the conf_commands
feature), nxt_cert_store_get() creates a buffer to send a certificate request
to the main process and adds its default completion handler to an asynchronous
queue to free the allocated buffer.  However, if configuration fails,
nxt_router_conf_error() removes the memory pool used to allocate the buffer,
causing a crash when the completion handler is dispatched.


Assertion "src/nxt_buf.c:208 assertion failed: data == b->parent" is triggered
when is NXT_DEBUG enabled in the configure script.


This patch uses a reference counter to retain the memory pool and redefines the
completion handler to free the buffer before releasing the memory pool.

src/nxt_cert.c

@@ -48,6 +48,7 @@ static nxt_conf_value_t *nxt_cert_name_details(nxt_mp_t *mp, X509 *x509,
     nxt_bool_t issuer);
 static nxt_conf_value_t *nxt_cert_alt_names_details(nxt_mp_t *mp,
     STACK_OF(GENERAL_NAME) *alt_names);
+static void nxt_cert_buf_completion(nxt_task_t *task, void *obj, void *data);
 
 
 static nxt_lvlhsh_t  nxt_cert_info;
@@ -1073,6 +1074,9 @@ nxt_cert_store_get(nxt_task_t *task, nxt_str_t *name, nxt_mp_t *mp,
         goto fail;
     }
 
+    nxt_mp_retain(mp);
+    b->completion_handler = nxt_cert_buf_completion;
+
     nxt_buf_cpystr(b, name);
     *b->mem.free++ = '\0';
 
@@ -1102,6 +1106,21 @@ fail:
 }
 
 
+static void
+nxt_cert_buf_completion(nxt_task_t *task, void *obj, void *data)
+{
+    nxt_mp_t   *mp;
+    nxt_buf_t  *b;
+
+    b = obj;
+    mp = b->data;
+    nxt_assert(b->next == NULL);
+
+    nxt_mp_free(mp, b);
+    nxt_mp_release(mp);
+}
+
+
 void
 nxt_cert_store_get_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
 {

src/nxt_router.c

@@ -773,7 +773,7 @@ fail:
                           msg->port_msg.stream, 0, NULL);
 
     if (tmcf != NULL) {
-        nxt_mp_destroy(tmcf->mem_pool);
+        nxt_mp_release(tmcf->mem_pool);
     }
 
 cleanup:
@@ -1061,7 +1061,7 @@ nxt_router_conf_ready(nxt_task_t *task, nxt_router_temp_conf_t *tmcf)
         nxt_mp_destroy(rtcf->mem_pool);
     }
 
-    nxt_mp_destroy(tmcf->mem_pool);
+    nxt_mp_release(tmcf->mem_pool);
 }
 
 
@@ -1120,7 +1120,7 @@ nxt_router_conf_error(nxt_task_t *task, nxt_router_temp_conf_t *tmcf)
 
     nxt_router_conf_send(task, tmcf, NXT_PORT_MSG_RPC_ERROR);
 
-    nxt_mp_destroy(tmcf->mem_pool);
+    nxt_mp_release(tmcf->mem_pool);
 }