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 B4B14C7EE23 for ; Tue, 16 May 2023 01:16:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229520AbjEPBQg (ORCPT ); Mon, 15 May 2023 21:16:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43910 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229493AbjEPBQb (ORCPT ); Mon, 15 May 2023 21:16:31 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 51A2E618D; Mon, 15 May 2023 18:16:30 -0700 (PDT) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4QKyrS6x6BzqSHQ; Tue, 16 May 2023 09:12:08 +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 09:16:27 +0800 Subject: Re: [PATCH v2 1/2] ovl: ovl_permission: Fix null pointer dereference at realinode in rcu-walk mode To: Amir Goldstein , Christian Brauner CC: , , References: <20230515133629.1974610-1-chengzhihao1@huawei.com> <20230515133629.1974610-2-chengzhihao1@huawei.com> <20230515-sprachen-zeltlager-6925dfbe19c1@brauner> <20230515-dulden-symmetrie-3b5d934478d4@brauner> From: Zhihao Cheng Message-ID: <53e81e0a-a99c-9a2a-7691-04789e2a2710@huawei.com> Date: Tue, 16 May 2023 09:16:26 +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: dggems706-chm.china.huawei.com (10.3.19.183) 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 2023/5/15 23:36, Amir Goldstein 写道: > On Mon, May 15, 2023 at 6:16 PM Christian Brauner wrote: >> >> On Mon, May 15, 2023 at 05:58:55PM +0300, Amir Goldstein wrote: >>> On Mon, May 15, 2023 at 4:58 PM Christian Brauner wrote: >>>> >>>> On Mon, May 15, 2023 at 09:36:28PM +0800, Zhihao Cheng wrote: >>>>> Following process: >>>>> P1 P2 >>>>> path_lookupat >>>>> link_path_walk >>>>> inode_permission >>>>> ovl_permission >>>>> ovl_i_path_real(inode, &realpath) >>>>> path->dentry = ovl_i_dentry_upper(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 >>>>> realinode = d_inode(realpath.dentry) // return NULL >>>>> inode_permission(realinode) >>>>> inode->i_sb // NULL pointer dereference >>>>> , will trigger an null pointer dereference at realinode: >>>>> [ 335.664979] BUG: kernel NULL pointer dereference, >>>>> address: 0000000000000002 >>>>> [ 335.668032] CPU: 0 PID: 2592 Comm: ls Not tainted 6.3.0 >>>>> [ 335.669956] RIP: 0010:inode_permission+0x33/0x2c0 >>>>> [ 335.678939] Call Trace: >>>>> [ 335.679165] >>>>> [ 335.679371] ovl_permission+0xde/0x320 >>>>> [ 335.679723] inode_permission+0x15e/0x2c0 >>>>> [ 335.680090] link_path_walk+0x115/0x550 >>>>> [ 335.680771] path_lookupat.isra.0+0xb2/0x200 >>>>> [ 335.681170] filename_lookup+0xda/0x240 >>>>> [ 335.681922] vfs_statx+0xa6/0x1f0 >>>>> [ 335.682233] vfs_fstatat+0x7b/0xb0 >>>>> >>>>> Fetch a reproducer in [Link]. >>>>> >>>>> Add a new helper ovl_i_path_realinode() to get realpath and real inode >>>>> after non-nullptr checking, use the helper to replace the current realpath >>>>> getting logic. >>>>> >>>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217405 >>>>> Fixes: 4b7791b2e958 ("ovl: handle idmappings in ovl_permission()") >>>>> Signed-off-by: Zhihao Cheng >>>>> Suggested-by: Christian Brauner >>>>> --- >>>>> fs/overlayfs/inode.c | 31 ++++++++++++++++++++++++------- >>>>> 1 file changed, 24 insertions(+), 7 deletions(-) >>>>> >>>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c >>>>> index 541cf3717fc2..cc3ef5a6666a 100644 >>>>> --- a/fs/overlayfs/inode.c >>>>> +++ b/fs/overlayfs/inode.c >>>>> @@ -278,6 +278,26 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path, >>>>> return err; >>>>> } >>>>> >>>>> +static inline int ovl_i_path_realinode(struct inode *inode, >>>>> + struct path *realpath, >>>>> + struct inode **realinode, int rcu) >>>>> +{ >>>>> + /* Careful in RCU walk mode */ >>>>> + ovl_i_path_real(inode, realpath); >>>>> + if (!realpath->dentry) { >>>>> + WARN_ON(!rcu); >>>>> + return -ECHILD; >>>>> + } >>>>> + >>>>> + *realinode = d_inode(realpath->dentry); >>>>> + if (!*realinode) { >>>>> + WARN_ON(!rcu); >>>>> + return -ECHILD; >>>>> + } >>>>> + >>>>> + return 0; >>>>> +} >>>> >>>> If you want to return the inode wouldn't it possibly make more sense to >>>> return the inode from the function directly? But not fuzzed. Maybe Amir >>>> has a preference. As I said, I'm even fine with the original approach. >>> >>> Sorry for not reviewing v1, I was traveling, even though it is hard to use >>> this excuse when I was traveling with Christian who did review v1 :) >> >> Well, I did only do it this morning. :) >> >>> >>>> >>>> static inline struct inode *ovl_i_path_realinode(struct inode *inode, >>>> struct path *realpath, >>>> int rcu) >>>> { >>>> struct inode *realinode; >>>> >>>> /* Careful in RCU walk mode */ >>>> ovl_i_path_real(inode, realpath); >>>> if (!realpath->dentry) { >>>> WARN_ON(!rcu); >>>> return ERR_PTR(-ECHILD); >>>> } >>>> >>>> realinode = d_inode(realpath->dentry); >>>> if (!realinode) { >>>> WARN_ON(!rcu); >>>> return ERR_PTR(-ECHILD); >>>> } >>>> >>>> return realinode; >>>> } >>>> >>> >>> I think this helper is over engineered ;-) >> >> Yes. As mentioned before, I would've been happy even with v1 that didn't >> have any helper. >> >>> The idea for a helper that returns inode is good, >>> but I see no reason to mix RCU walk in this helper >>> and don't even need a new helper (see untested patch below). >> >> Looks good to me too. >> >>> >>> Thanks, >>> Amir. >>> >>> --- >>> -void ovl_i_path_real(struct inode *inode, struct path *path) >>> +struct inode *ovl_i_path_real(struct inode *inode, struct path *path) >>> { >>> struct ovl_path *lowerpath = ovl_lowerpath(OVL_I_E(inode)); >>> >>> @@ -342,6 +342,8 @@ void ovl_i_path_real(struct inode *inode, struct path *path) >>> } else { >>> path->mnt = ovl_upper_mnt(OVL_FS(inode->i_sb)); >>> } >>> + >>> + return path->dentry ? d_inode(path->dentry) : NULL; >>> } >>> >>> @@ -295,8 +295,8 @@ int ovl_permission(struct mnt_idmap *idmap, >>> int err; >>> >>> /* Careful in RCU walk mode */ >>> - ovl_i_path_real(inode, &realpath); >>> - if (!realpath.dentry) { >>> + realinode = ovl_i_path_real(inode, &realpath); >>> + if (!realpath.dentry || !realinode) { >>> WARN_ON(!(mask & MAY_NOT_BLOCK)); >>> return -ECHILD; >>> } >>> @@ -309,7 +309,6 @@ int ovl_permission(struct mnt_idmap *idmap, >>> >>> if (err) >>> return err; >>> >>> - realinode = d_inode(realpath.dentry); >>> old_cred = ovl_override_creds(inode->i_sb); >> Thanks for reviewings and helpful discussion from Amir and Christian. >> Btw, if the reproducer that Zhihao has posted in the bugzilla link: >> >> #!/bin/bash >> >> mkdir -p /root/tmp/merge /root/tmp/upper/dir /root/tmp/lower /root/tmp/work >> touch /root/tmp/upper/dir/file >> chown freg:freg -R /root/tmp/upper/dir >> mount -t overlay none -oupperdir=/root/tmp/upper,lowerdir=/root/tmp/lower,workdir=/root/tmp/work /root/tmp/merge >> ls /root/tmp/merge/dir/file & >> echo 3 > /proc/sys/vm/drop_caches >> >> is reliable we should add it to xfstests... > > If only it was that easy to trigger this race. > Look at the debug kernel patch named 'diff' in bugzilla... Yes, I can hardly reproduce the problem without the time delay in kernel. > > Thanks, > Amir. > . >