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 6F494C77B7A for ; Tue, 16 May 2023 12:27:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233086AbjEPM1v (ORCPT ); Tue, 16 May 2023 08:27:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229664AbjEPM1s (ORCPT ); Tue, 16 May 2023 08:27:48 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A586B5BBC; Tue, 16 May 2023 05:27:41 -0700 (PDT) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4QLFkv68blzqSJ4; Tue, 16 May 2023 20:23:19 +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 20:27:38 +0800 Subject: Re: [PATCH v2 1/2] ovl: ovl_permission: Fix null pointer dereference at realinode in rcu-walk mode To: Amir Goldstein CC: Christian Brauner , , , References: <20230515133629.1974610-1-chengzhihao1@huawei.com> <20230515133629.1974610-2-chengzhihao1@huawei.com> <20230515-sprachen-zeltlager-6925dfbe19c1@brauner> <20230515-dulden-symmetrie-3b5d934478d4@brauner> <53e81e0a-a99c-9a2a-7691-04789e2a2710@huawei.com> From: Zhihao Cheng Message-ID: <06361c3e-9f78-6f44-9cd0-e39e1eb9c546@huawei.com> Date: Tue, 16 May 2023 20:27:38 +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 19:45, Amir Goldstein 写道: > On Tue, May 16, 2023 at 4:16 AM Zhihao Cheng wrote: >> >> 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. >> > > You're welcome. > > Note to self: there is be a trivial conflict with the change to > ovl_i_path_real() > return type and this patch from my ovl-lazy-lowerdata series: > https://lore.kernel.org/linux-unionfs/20230427130539.2798797-7-amir73il@gmail.com/ > > After Miklos takes your fixes, I will rebase. Thanks for rebasing, so you will take v2 with modified helper ovl_i_path_real(return realinode)? > > Thanks, > Amir. > . >