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 DC772C7EE23 for ; Tue, 16 May 2023 12:25:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232218AbjEPMZf (ORCPT ); Tue, 16 May 2023 08:25:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44096 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229664AbjEPMZd (ORCPT ); Tue, 16 May 2023 08:25:33 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C529049F5; Tue, 16 May 2023 05:25:30 -0700 (PDT) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.53]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4QLFhP1Nslz18LWG; Tue, 16 May 2023 20:21:09 +0800 (CST) Received: from [10.174.178.46] (10.174.178.46) by kwepemm600013.china.huawei.com (7.193.23.68) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Tue, 16 May 2023 20:25:27 +0800 Subject: Re: [PATCH v2 2/2] ovl: get_acl: Fix null pointer dereference at realinode in rcu-walk mode To: Amir Goldstein CC: , , , References: <20230515133629.1974610-1-chengzhihao1@huawei.com> <20230515133629.1974610-3-chengzhihao1@huawei.com> From: Zhihao Cheng Message-ID: <1f11e2f3-bdf8-553c-82fa-b24619e28e73@huawei.com> Date: Tue, 16 May 2023 20:25:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.46] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To kwepemm600013.china.huawei.com (7.193.23.68) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2023/5/16 19:40, Amir Goldstein 写道: > On Mon, May 15, 2023 at 4:39 PM Zhihao Cheng wrote: >> >> Following process: >> P1 P2 >> path_openat >> link_path_walk >> may_lookup >> inode_permission(rcu) >> ovl_permission >> acl_permission_check >> check_acl >> get_cached_acl_rcu >> ovl_get_inode_acl >> realinode = ovl_inode_real(ovl_inode) >> drop_cache >> __dentry_kill(ovl_dentry) >> iput(ovl_inode) >> ovl_destroy_inode(ovl_inode) >> dput(oi->__upperdentry) >> dentry_kill(upperdentry) >> dentry_unlink_inode >> upperdentry->d_inode = NULL >> ovl_inode_upper >> upperdentry = ovl_i_dentry_upper(ovl_inode) >> d_inode(upperdentry) // returns NULL >> IS_POSIXACL(realinode) // NULL pointer dereference >> , will trigger an null pointer dereference at realinode: >> [ 205.472797] BUG: kernel NULL pointer dereference, address: >> 0000000000000028 >> [ 205.476701] CPU: 2 PID: 2713 Comm: ls Not tainted >> 6.3.0-12064-g2edfa098e750-dirty #1216 >> [ 205.478754] RIP: 0010:do_ovl_get_acl+0x5d/0x300 >> [ 205.489584] Call Trace: >> [ 205.489812] >> [ 205.490014] ovl_get_inode_acl+0x26/0x30 >> [ 205.490466] get_cached_acl_rcu+0x61/0xa0 >> [ 205.490908] generic_permission+0x1bf/0x4e0 >> [ 205.491447] ovl_permission+0x79/0x1b0 >> [ 205.491917] inode_permission+0x15e/0x2c0 >> [ 205.492425] link_path_walk+0x115/0x550 >> [ 205.493311] path_lookupat.isra.0+0xb2/0x200 >> [ 205.493803] filename_lookup+0xda/0x240 >> [ 205.495747] vfs_fstatat+0x7b/0xb0 >> >> Fetch a reproducer in [Link]. >> >> Fix it by using helper ovl_i_path_realinode() to get realpath and real >> inode after non-nullptr checking. >> >> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217404 >> Fixes: 332f606b32b6 ("ovl: enable RCU'd ->get_acl()") > > Note that this bug is also in 5.15.y, in method ovl_get_acl(). > I hope you will be able to follow up with a simple backport for 5.15 - > i.e. only need to add a check for NULL realinode at the beginning. > There was no realpath back then. > Sure. I notice that there is a '[ Upstream commit xxx ]' field in 5.15 patch, so may I backport it after the fix applied into mainline(6.4)? > AFAICT, both your patches should apply cleanly to 6.1.y, so should > be picked up automatically by stable kernel bots. > > Thanks, > Amir. > >> Signed-off-by: Zhihao Cheng >> Suggested-by: Christian Brauner >> --- >> fs/overlayfs/inode.c | 14 ++++++-------- >> 1 file changed, 6 insertions(+), 8 deletions(-) >> >> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c >> index cc3ef5a6666a..b2021eada8be 100644 >> --- a/fs/overlayfs/inode.c >> +++ b/fs/overlayfs/inode.c >> @@ -576,20 +576,18 @@ struct posix_acl *do_ovl_get_acl(struct mnt_idmap *idmap, >> struct inode *inode, int type, >> bool rcu, bool noperm) >> { >> - struct inode *realinode = ovl_inode_real(inode); >> + struct inode *realinode; >> struct posix_acl *acl; >> struct path realpath; >> + int err; >> + >> + err = ovl_i_path_realinode(inode, &realpath, &realinode, rcu); >> + if (err) >> + return ERR_PTR(err); >> >> if (!IS_POSIXACL(realinode)) >> return NULL; >> >> - /* Careful in RCU walk mode */ >> - ovl_i_path_real(inode, &realpath); >> - if (!realpath.dentry) { >> - WARN_ON(!rcu); >> - return ERR_PTR(-ECHILD); >> - } >> - >> if (rcu) { >> /* >> * If the layer is idmapped drop out of RCU path walk >> -- >> 2.39.2 >> > . >