From mboxrd@z Thu Jan 1 00:00:00 1970 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 F0B9AC433F5 for ; Mon, 28 Mar 2022 21:26:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229949AbiC1V2b (ORCPT ); Mon, 28 Mar 2022 17:28:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59476 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229502AbiC1V23 (ORCPT ); Mon, 28 Mar 2022 17:28:29 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AE4B913DB7B for ; Mon, 28 Mar 2022 14:26:40 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id D54D6CE13BA for ; Mon, 28 Mar 2022 21:26:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDD87C340F0; Mon, 28 Mar 2022 21:26:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1648502790; bh=wxoq9ME/nIVvmUovBMwsQE6E8oPpAYoAac/ZEw8Fya0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=yf2w62tXhWPSCdrwhr8ccax+GVrf2ywD2KQk2KtH9HUhQmdXMDPoZJ5V4UvoTySq2 udT2dg8Ev7lBimxMk1Yq0bG3gGeCJIEKACvs4H2DV+ytQ3vhyr2qVP3V3iBJMJqaSl UGQFD1P1IKswDwMgGsYlOLpcmpYHzqAkQk+kHK+Y= Date: Mon, 28 Mar 2022 14:26:29 -0700 From: Andrew Morton To: Miaohe Lin Cc: , , , , Subject: Re: [PATCH v3] mm/mempolicy: fix mpol_new leak in shared_policy_replace Message-Id: <20220328142629.6ab7c5312d9ec154ccc502b2@linux-foundation.org> In-Reply-To: References: <20220322104345.36379-1-linmiaohe@huawei.com> <20220325172907.57dd381b746563be5dc77097@linux-foundation.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 26 Mar 2022 14:46:28 +0800 Miaohe Lin wrote: > On 2022/3/26 8:29, Andrew Morton wrote: > > On Tue, 22 Mar 2022 18:43:45 +0800 Miaohe Lin wrote: > > > >> 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 = shmget((key_t)5566, 1024 * PAGE_SIZE, 0666|IPC_CREAT); > >> shm = 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); > >> } > >> > >> ... > >> > >> --- 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 = kmem_cache_alloc(policy_cache, GFP_KERNEL); > >> if (!mpol_new) > >> goto err_out; > >> + refcount_set(&mpol_new->refcnt, 1); > >> goto restart; > >> } > > > > Two other sites in this file do > > > > atomic_set(&policy->refcnt, 1); > > > > > > Could we please instead have a little helper function which does the > > kmem_cache_alloc()+refcount_set()?> . > > There are usecases like below: > > struct mempolicy *new = kmem_cache_alloc(policy_cache, GFP_KERNEL); > *new = *old; > ^^^^^^^^^^^^ > refcount_set(&new->refcnt, 1); > > If we use helper function to do kmem_cache_alloc()+refcount_set() above, separate > refcount_set(&new->refcnt, 1) is still needed as old is copied to new and overwrites > the refcnt field. So that little helper function might not work. Or am I miss something? > Hm, spose so. I guess the helper doesn't add much in that case. Can we please redo this on mainline? I'm not happy with the bloat which refcnt_t adds and I think I'll drop mm-mempolicy-convert-from-atomic_t-to-refcount_t-on-mempolicy-refcnt.patch.