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Thu, 9 Dec 2021 20:13:11 +0000 (GMT) Message-ID: Date: Thu, 9 Dec 2021 15:13:11 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace Content-Language: en-US To: jejb@linux.ibm.com, Christian Brauner Cc: linux-integrity@vger.kernel.org, zohar@linux.ibm.com, serge@hallyn.com, containers@lists.linux.dev, dmitry.kasatkin@gmail.com, ebiederm@xmission.com, krzysztof.struczynski@huawei.com, roberto.sassu@huawei.com, mpeters@redhat.com, lhinds@redhat.com, lsturman@redhat.com, puiterwi@redhat.com, jamjoom@us.ibm.com, linux-kernel@vger.kernel.org, paul@paul-moore.com, rgb@redhat.com, linux-security-module@vger.kernel.org, jmorris@namei.org References: <20211208221818.1519628-1-stefanb@linux.ibm.com> <20211208221818.1519628-16-stefanb@linux.ibm.com> <20211209143428.ip6bwry5hqtee5vy@wittgenstein> <20211209143749.wk4agkynfqdzftbl@wittgenstein> From: Stefan Berger In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 5rQG5iYqb71RF1kGPemKOzU5RL2Lp7oW X-Proofpoint-ORIG-GUID: QSmYg_siB4Boj2NCDH0480Emj7m4TrV_ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2021-12-09_08,2021-12-08_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 priorityscore=1501 mlxscore=0 phishscore=0 lowpriorityscore=0 spamscore=0 suspectscore=0 bulkscore=0 malwarescore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2112090104 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/9/21 14:38, James Bottomley wrote: > On Thu, 2021-12-09 at 10:30 -0500, James Bottomley wrote: >> On Thu, 2021-12-09 at 15:37 +0100, Christian Brauner wrote: >>> On Thu, Dec 09, 2021 at 03:34:28PM +0100, Christian Brauner wrote: >>>> On Wed, Dec 08, 2021 at 05:18:17PM -0500, Stefan Berger wrote: >>>>> Move the dentries into the ima_namespace for reuse by >>>>> virtualized >>>>> SecurityFS. Implement function freeing the dentries in order of >>>>> files and symlinks before directories. >>>>> >>>>> Signed-off-by: Stefan Berger >>>>> --- >>>> This doesn't work as implemented, I think. >>>> >>>> What I would have preferred and what I tried to explain in the >>>> earlier review was: >>>> Keep the dentry stashing global since it is only needed for >>>> init_ima_ns. >>>> Then struct ima_namespace becomes way smaller and simpler. >>>> If you do that then it makes sense to remove the additional >>>> dget() in securityfs_create_dentry() for non-init_ima_ns. >>>> Then you can rely on auto-cleanup in .kill_sb() or on >>>> ima_securityfs_init() failure and you only need to call >>>> ima_fs_ns_free_dentries() if ns != init_ima_ns. >>>> >>>> IIuc, it seems you're currently doing one dput() too many since >>>> you're calling securityfs_remove() in the error path for non- >>>> init_ima_ns which relies on the previous increased dget() which >>>> we removed. >>> If you really want to move the dentry stashing into struct >>> ima_namespace even though it's really unnecessary then you may as >>> well not care about the auto-cleanup and keep that additional >>> ima_fs_ns_free_dentries(ns) call in .kill_sb(). But I really think >>> not dragging dentry stashing into struct ima_namespace is the >>> correct way to go about this. >> We, unfortunately, do have one case we can't avoid stashing for the >> policy file. It's this code in ima_release_policy: >> >>> #if !defined(CONFIG_IMA_WRITE_POLICY) && >>> !defined(CONFIG_IMA_READ_POLICY) >>> securityfs_remove(ns->dentry[IMAFS_DENTRY_IMA_POLICY]); >>> ns->dentry[IMAFS_DENTRY_IMA_POLICY] = NULL; >>> >> What it does is that in certain config options, the policy file entry >> gets removed from the securityfs ima directory after you write to it. > This is what I have incremental to v5 that corrects all of this. It > actually keeps every dentry reference (including init_user_ns ones) at > 1 so they can be reaped on unmount. For the remove case it does > d_delete and then puts the only reference. This means > securityfs_remove() works for the namespaced policy file as well. I fixed it now as well but do another dget() on securityfs_removed() for ns != init_user_ns. Ok, I will add what you have below. > > I also got rid of the spurious initialized check in ima_securityfs_init > because it prevents you doing a mount;umount;mount on securityfs within > a namespace. > > There's still the problem that if you write the policy, making the file > disappear then unmount and remount securityfs it will come back. My > guess for fixing this is that we only stash the policy file reference, > create it if NULL but then set the pointer to PTR_ERR(-EINVAL) or > something and refuse to create it for that value. What about boolean to remember this? I just added this. > > James > > --- > > From 7de285a81ff06b6e0eb2c6db24810aeef9f6dd17 Mon Sep 17 00:00:00 2001 > From: James Bottomley > Date: Thu, 9 Dec 2021 19:33:49 +0000 > Subject: [PATCH] fix dentry ref counting > > --- > security/inode.c | 12 ++---------- > security/integrity/ima/ima_fs.c | 4 ---- > 2 files changed, 2 insertions(+), 14 deletions(-) > > diff --git a/security/inode.c b/security/inode.c > index eaccba7017d9..b53152f7a625 100644 > --- a/security/inode.c > +++ b/security/inode.c > @@ -178,8 +178,6 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode, > inode->i_fop = fops; > } > d_instantiate(dentry, inode); > - if (ns == &init_user_ns) > - dget(dentry); > inode_unlock(dir); > return dentry; > > @@ -317,21 +315,15 @@ EXPORT_SYMBOL_GPL(securityfs_create_symlink); > void securityfs_remove(struct dentry *dentry) > { > struct user_namespace *ns = dentry->d_sb->s_user_ns; > - struct inode *dir; > > if (!dentry || IS_ERR(dentry)) > return; > > - dir = d_inode(dentry->d_parent); > - inode_lock(dir); > if (simple_positive(dentry)) { > - if (d_is_dir(dentry)) > - simple_rmdir(dir, dentry); > - else > - simple_unlink(dir, dentry); > + d_delete(dentry); > dput(dentry); > } > - inode_unlock(dir); > + > if (ns == &init_user_ns) > simple_release_fs(&init_securityfs_mount, > &init_securityfs_mount_count); > diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c > index 778983fd9a73..077a6ff46858 100644 > --- a/security/integrity/ima/ima_fs.c > +++ b/security/integrity/ima/ima_fs.c > @@ -466,10 +466,6 @@ int ima_securityfs_init(struct user_namespace *user_ns, struct dentry *root) > struct ima_namespace *ns = user_ns->ima_ns; > struct dentry *ima_dir; > > - /* already initialized? */ > - if (ns->dentry[IMAFS_DENTRY_INTEGRITY_DIR]) > - return 0; > - > /* FIXME: update when evm and integrity are namespaced */ > if (user_ns != &init_user_ns) { > ns->dentry[IMAFS_DENTRY_INTEGRITY_DIR] =