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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88921C433EF for ; Sat, 26 Mar 2022 00:29:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B97FE6B0072; Fri, 25 Mar 2022 20:29:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B459A6B0073; Fri, 25 Mar 2022 20:29:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A34646B0074; Fri, 25 Mar 2022 20:29:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0148.hostedemail.com [216.40.44.148]) by kanga.kvack.org (Postfix) with ESMTP id 9060F6B0072 for ; Fri, 25 Mar 2022 20:29:10 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 34A3EA5A77 for ; Sat, 26 Mar 2022 00:29:10 +0000 (UTC) X-FDA: 79284652860.29.91A8BF8 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf27.hostedemail.com (Postfix) with ESMTP id AC3A64002D for ; Sat, 26 Mar 2022 00:29:09 +0000 (UTC) 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 dfw.source.kernel.org (Postfix) with ESMTPS id C1EF1617C4; Sat, 26 Mar 2022 00:29:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1C29C2BBE4; Sat, 26 Mar 2022 00:29:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1648254548; bh=AnJgnpPYiCm5oGyGAtaAtR44bfRlNgR5d1iIOGU/Fh4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=wluuJcBvB4K5JpO4od1HeDpdOd4INTC11C7xHzJZF7N0ZtWak2j1uXHelhzQC26bR Xdp5n+iQBdyeu4Anen+QGCjCF+/IbIgpk1L0yj2yj3YI/2HAKiuS+rUFwPbcvIx+iC Dybf4+chRqkGiZRRBrRFatwAP3JU+8vf4mreejYE= Date: Fri, 25 Mar 2022 17:29:07 -0700 From: Andrew Morton To: Miaohe Lin Cc: , , , , Subject: Re: [PATCH v3] mm/mempolicy: fix mpol_new leak in shared_policy_replace Message-Id: <20220325172907.57dd381b746563be5dc77097@linux-foundation.org> In-Reply-To: <20220322104345.36379-1-linmiaohe@huawei.com> References: <20220322104345.36379-1-linmiaohe@huawei.com> 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 X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: AC3A64002D X-Rspam-User: Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=wluuJcBv; dmarc=none; spf=pass (imf27.hostedemail.com: domain of akpm@linux-foundation.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Stat-Signature: h5xfucn6k5gzd5ygctktgyngnt1b1kii X-HE-Tag: 1648254549-866795 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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()?