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Thu, 4 Feb 2021 16:32:24 +0000 To: Michal Hocko , LKML From: =?UTF-8?Q?Christian_K=c3=b6nig?= Subject: Possible deny of service with memfd_create() Message-ID: Date: Thu, 4 Feb 2021 17:32:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [2a02:908:1252:fb60:be8a:bd56:1f94:86e7] X-ClientProxiedBy: AM0PR04CA0043.eurprd04.prod.outlook.com (2603:10a6:208:1::20) To MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2a02:908:1252:fb60:be8a:bd56:1f94:86e7] (2a02:908:1252:fb60:be8a:bd56:1f94:86e7) by AM0PR04CA0043.eurprd04.prod.outlook.com (2603:10a6:208:1::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3825.17 via Frontend Transport; Thu, 4 Feb 2021 16:32:23 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-HT: Tenant X-MS-Office365-Filtering-Correlation-Id: f0fa78aa-1d66-4062-e5e5-08d8c92a739a X-MS-TrafficTypeDiagnostic: MN2PR12MB4254: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:7219; 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The issue is that the memory allocated for the file descriptor is not accounted to the process allocating it, so the OOM killer pics whatever process it things is good but never my small test program. Since memfd_create() doesn't need any special permission this is a rather nice deny of service and as far as I can see also works with a standard Ubuntu 5.4.0-65-generic kernel. Cheers, Christian. #define _GNU_SOURCE #include #include #include unsigned char page[4096]; int main(void) {         int i, fd;         for (i = 0; i < 4096; ++i)                 page[i] = i;         fd = memfd_create("test", 0);         while (1)                 write(fd, page, 4096); }