Make sure to modify memory_limit value through the registered handler.

Author: manuelm

main/main.c

@@ -381,8 +381,8 @@ static PHP_INI_MH(OnChangeMaxMemoryLimit)
 		return FAILURE;
 	}
 
-	PG(memory_limit) = value;
 	PG(max_memory_limit) = value;
+	zend_alter_ini_entry(ZSTR_INIT_LITERAL("memory_limit", 1), new_value, PHP_INI_ALL, stage);
 
 	return SUCCESS;
 }

sapi/fpm/tests/gh17951-restore-memory-limit.phpt

@@ -0,0 +1,73 @@
+--TEST--
+FPM: GH-17951 - make sure to restore implicit memory_limit
+--SKIPIF--
+<?php include "skipif.inc"; ?>
+--FILE--
+<?php
+
+require_once "tester.inc";
+
+$cfg = <<<EOT
+[global]
+error_log = {{FILE:LOG}}
+[unconfined]
+listen = {{ADDR}}
+pm = dynamic
+pm.max_children = 5
+pm.start_servers = 1
+pm.min_spare_servers = 1
+pm.max_spare_servers = 3
+EOT;
+
+$ini = <<<EOT
+max_memory_limit = 100M
+[HOST=foo.bar]
+max_memory_limit = 200M
+[HOST=bar.foo]
+max_memory_limit = 300M
+EOT;
+
+$code = <<<EOT
+<?php
+echo "Test Start\n";
+var_dump(ini_get('memory_limit'));
+echo "Test End\n";
+EOT;
+
+$tester = new FPM\Tester($cfg, $code);
+$tester->start(iniEntries: $ini);
+$tester->expectLogStartNotices();
+$tester->request()->expectBody([
+    'Test Start',
+    'string(4) "100M"',
+    'Test End'
+]);
+$tester->request(headers: [ "SERVER_NAME" => "foo.bar" ])->expectBody([
+    'Test Start',
+    'string(4) "200M"',
+    'Test End'
+]);
+$tester->request(headers: [ "SERVER_NAME" => "bar.foo" ])->expectBody([
+    'Test Start',
+    'string(4) "300M"',
+    'Test End'
+]);
+# check if the ini value has been reset
+$tester->request()->expectBody([
+    'Test Start',
+    'string(4) "100M"',
+    'Test End'
+]);
+$tester->terminate();
+$tester->expectLogTerminatingNotices();
+$tester->close();
+
+?>
+Done
+--EXPECT--
+Done
+--CLEAN--
+<?php
+require_once "tester.inc";
+FPM\Tester::clean();
+?>