Prevent execution of install_hook() hooks after disabling tracer (#2016)

This led to crashes in combination with the database integrations, if database calls happened after the tracer was disabled.

Signed-off-by: Bob Weinand <bob.weinand@datadoghq.com>

ext/hook/uhook.c

@@ -178,7 +178,7 @@ static bool dd_uhook_begin(zend_ulong invocation, zend_execute_data *execute_dat
     dd_uhook_def *def = auxiliary;
     dd_uhook_dynamic *dyn = dynamic;
 
-    if (def->closure && def->closure != ZEND_CLOSURE_OBJECT(EX(func))) {
+    if ((def->closure && def->closure != ZEND_CLOSURE_OBJECT(EX(func))) || !get_DD_TRACE_ENABLED()) {
         dyn->hook_data = NULL;
         return true;
     }
@@ -219,7 +219,7 @@ static void dd_uhook_end(zend_ulong invocation, zend_execute_data *execute_data,
         dd_trace_stop_span_time(span);
     }
 
-    if (def->end && !def->running) {
+    if (def->end && !def->running && get_DD_TRACE_ENABLED()) {
         zval tmp;
 
         /* If the profiler doesn't handle a potential pending interrupt before
@@ -480,7 +480,7 @@ void dd_uhook_span(INTERNAL_FUNCTION_PARAMETERS, bool unlimited) {
     }
 
     // pre-hook check
-    if (!hookData->execute_data || (!unlimited && ddtrace_tracer_is_limited())) {
+    if (!hookData->execute_data || (!unlimited && ddtrace_tracer_is_limited()) || !get_DD_TRACE_ENABLED()) {
         // dummy span, which never gets pushed
         hookData->span = ddtrace_init_dummy_span();
         RETURN_OBJ_COPY(&hookData->span->std);

tests/ext/sandbox/install_hook/hook_not_invoked_if_tracer_disabled.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Ensure hooks are not invoked after the tracer has been disabled
+--FILE--
+<?php
+
+function foo() {}
+DDTrace\install_hook("foo", function($h) {
+    print "Invoked\n";
+    ini_set("datadog.trace.enabled", 0);
+    $h->span(); // must not crash
+}, function() {
+    print "Skipped\n";
+});
+foo();
+foo();
+
+?>
+--EXPECT--
+Invoked