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Fri, 10 Dec 2021 15:26:50 +0000 (GMT) Received: from sig-9-65-75-5.ibm.com (unknown [9.65.75.5]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 10 Dec 2021 15:26:50 +0000 (GMT) Message-ID: Subject: Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace From: Mimi Zohar To: jejb@linux.ibm.com, Stefan Berger , Christian Brauner Cc: linux-integrity@vger.kernel.org, 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 Date: Fri, 10 Dec 2021 10:26:50 -0500 In-Reply-To: References: <20211208221818.1519628-1-stefanb@linux.ibm.com> <20211208221818.1519628-16-stefanb@linux.ibm.com> <20211209143428.ip6bwry5hqtee5vy@wittgenstein> <20211209143749.wk4agkynfqdzftbl@wittgenstein> <20211210114934.tacjnwryihrsx6ln@wittgenstein> <2587716d7d021c35e3b6ef22b6e30f44c2b3f98e.camel@linux.ibm.com> <6de8d349-74f8-7be4-3854-5c4ac72860ad@linux.ibm.com> <66b377f6-40b4-77da-c02b-2650fa72d0b4@linux.ibm.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.28.5 (3.28.5-18.el8) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 6CR5zTzixK_mjnBB8zlNK9KeAY-TRWHF X-Proofpoint-GUID: f0kVUSY7_3sRnJebrTmG4W4mThrrhNe5 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=2021-12-10_05,2021-12-10_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 spamscore=0 impostorscore=0 mlxscore=0 mlxlogscore=999 lowpriorityscore=0 malwarescore=0 adultscore=0 suspectscore=0 priorityscore=1501 clxscore=1015 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2112100086 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2021-12-10 at 09:26 -0500, James Bottomley wrote: > On Fri, 2021-12-10 at 09:17 -0500, Stefan Berger wrote: > > On 12/10/21 08:02, Mimi Zohar wrote: > > > On Fri, 2021-12-10 at 07:40 -0500, Stefan Berger wrote: > > > > On 12/10/21 07:09, Mimi Zohar wrote: > > > > > On Fri, 2021-12-10 at 12:49 +0100, Christian Brauner wrote: > > > > > > > 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. > > > > > > Some sort of indicator that gets stashed in struct ima_ns > > > > > > that the file does not get recreated on consecutive mounts. > > > > > > That shouldn't be hard to fix. > > > > > The policy file disappearing is for backwards compatibility, > > > > > prior to being able to extend the custom policy. For embedded > > > > > usecases, allowing the policy to be written exactly once might > > > > > makes sense. Do we really want/need to continue to support > > > > > removing the policy in namespaces? > > > > I don't have an answer but should the behavior for the same > > > > #define in this case be different for host and namespaces? Or > > > > should we just 'select IMA_WRITE_POLICY and IMA_READ_POLICY' when > > > > IMA_NS is selected? > > > The latter option sounds good. Being able to analyze the namespace > > > policy is really important. > > > > Ok, I will adjust the Kconfig for this then. This then warrants the > > question whether to move the dentry into the ima_namespace. The > > current code looks like this. > > > > #if !defined(CONFIG_IMA_WRITE_POLICY) && > > !defined(CONFIG_IMA_READ_POLICY) > > securityfs_remove(ns->policy_dentry); > > ns->policy_dentry = NULL; > > ns->policy_dentry_removed = true; > > #elif defined(CONFIG_IMA_WRITE_POLICY) > > > > With IMA_NS selecting IMA_WRITE_POLICY and IMA_READ_POLICY the above > > wouldn't be necessary anymore but I find it 'cleaner' to still have > > the dentry isolated rather than it being a global static as it was > > before... > > This is really, really why you don't want the semantics inside the > namespace to differ from those outside, because it creates confusion > for the people reading the code, especially with magically forced > config options like this. I'd strongly suggest you either keep the > semantic in the namespace or eliminate it entirely. > > If you really, really have to make the namespace behave differently, > then use global variables and put a big comment on that code saying it > can never be reached once CONFIG_IMA_NS is enabled. The problem seems to be with removing the securityfs policy file. Instead of removing it, just make it inacessible for the "if !defined(CONFIG_IMA_WRITE_POLICY) && !defined(CONFIG_IMA_READ_POLICY)" case. thanks, Mimi