From nobody Sun Jun 21 10:22:50 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58F2DC433F5 for ; Tue, 29 Mar 2022 11:13:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235596AbiC2LPf (ORCPT ); Tue, 29 Mar 2022 07:15:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33542 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232456AbiC2LPd (ORCPT ); Tue, 29 Mar 2022 07:15:33 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D761B3CFD9 for ; Tue, 29 Mar 2022 04:13:47 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KSRkw57JZzcZyX; Tue, 29 Mar 2022 19:13:28 +0800 (CST) Received: from huawei.com (10.175.124.27) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Tue, 29 Mar 2022 19:13:44 +0800 From: Miaohe Lin To: , CC: , , , , Subject: [PATCH v4] mm/mempolicy: fix mpol_new leak in shared_policy_replace Date: Tue, 29 Mar 2022 19:14:16 +0800 Message-ID: <20220329111416.27954-1-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.175.124.27] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" If mpol_new is allocated but not used in restart loop, mpol_new will be freed via mpol_put before returning to the caller. But refcnt is not initialized yet, so mpol_put could not do the right things and might leak the unused mpol_new. This would happen if mempolicy was updated on the shared shmem file while the sp->lock has been dropped during the memory allocation. This issue could be triggered easily with the below code snippet if there are many processes doing the below work at the same time: shmid =3D shmget((key_t)5566, 1024 * PAGE_SIZE, 0666|IPC_CREAT); shm =3D shmat(shmid, 0, 0); loop many times { mbind(shm, 1024 * PAGE_SIZE, MPOL_LOCAL, mask, maxnode, 0); mbind(shm + 128 * PAGE_SIZE, 128 * PAGE_SIZE, MPOL_DEFAULT, mask, maxnode, 0); } Fixes: 42288fe366c4 ("mm: mempolicy: Convert shared_policy mutex to spinloc= k") Signed-off-by: Miaohe Lin Acked-by: Michal Hocko Cc: # 3.8 --- v3->v4: rebase on mainline. v2->v3: enhance commit log and collect Acked-by tag per Michal Hocko. Thanks! v1->v2: Add reproducer snippet and Cc stable. Thanks Michal Hocko for review and comment! --- mm/mempolicy.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index a2516d31db6c..6b34c5d5e65a 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2733,6 +2733,7 @@ static int shared_policy_replace(struct shared_policy= *sp, unsigned long start, mpol_new =3D kmem_cache_alloc(policy_cache, GFP_KERNEL); if (!mpol_new) goto err_out; + atomic_set(&mpol_new->refcnt, 1); goto restart; } =20 --=20 2.23.0