Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <2e493258-b267-b8ad-0812-53f4e9c849ae@huaweicloud.com>
Date:   Fri, 18 Nov 2022 10:32:15 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.2.0
Subject: Re: [PATCH v4 3/5] security: Allow all LSMs to provide xattrs for
 inode_init_security hook
Content-Language: en-US
To:     Casey Schaufler <casey@schaufler-ca.com>,
        Mimi Zohar <zohar@linux.ibm.com>, dmitry.kasatkin@gmail.com,
        paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com,
        stephen.smalley.work@gmail.com, eparis@parisplace.org
Cc:     linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
        reiserfs-devel@vger.kernel.org, linux-kernel@vger.kernel.org,
        keescook@chromium.org, nicolas.bouchinet@clip-os.org,
        Roberto Sassu <roberto.sassu@huawei.com>
References: <20221110094639.3086409-1-roberto.sassu@huaweicloud.com>
 <20221110094639.3086409-4-roberto.sassu@huaweicloud.com>
 <4c1349f670dc3c23214a5a5036e43ddaa0a7bc89.camel@linux.ibm.com>
 <026075fa-0b58-9041-0727-b75e19499356@schaufler-ca.com>
From:   Roberto Sassu <roberto.sassu@huaweicloud.com>
In-Reply-To: <026075fa-0b58-9041-0727-b75e19499356@schaufler-ca.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 11/17/2022 6:18 PM, Casey Schaufler wrote:
> On 11/17/2022 8:05 AM, Mimi Zohar wrote:
>> hOn Thu, 2022-11-10 at 10:46 +0100, Roberto Sassu wrote:
>>> From: Roberto Sassu <roberto.sassu@huawei.com>
>>>
>>> Currently, security_inode_init_security() supports only one LSM providing
>>> an xattr and EVM calculating the HMAC on that xattr, plus other inode
>>> metadata.
>>>
>>> Allow all LSMs to provide one or multiple xattrs, by extending the security
>>> blob reservation mechanism. Introduce the new lbs_xattr field of the
>>> lsm_blob_sizes structure, so that each LSM can specify how many xattrs it
>>> needs, and the LSM infrastructure knows how many xattr slots it should
>>> allocate.
>> Perhaps supporting per LSM multiple xattrs is a nice idea, but EVM
>> doesn't currently support it.  The LSM xattrs are hard coded in
>> evm_config_default_xattrnames[],  based on whether the LSM is
>> configured.  Additional security xattrs may be included in the
>> security.evm calculation, by extending the list via
>> security/integrity/evm/evm_xattrs.
> 
> Smack uses multiple xattrs. All file system objects have a SMACK64
> attribute, which is used for access control. A program file may have
> a SMACK64EXEC attribute, which is the label the program will run with.
> A library may have a SMACK64MMAP attribute to restrict loading. A
> directory may have a SMACK64TRANSMUTE attribute, which modifies the
> new object creation behavior.
> 
> The point being that it may be more than a "nice idea" to support
> multiple xattrs. It's not a hypothetical situation.

Ok, that means that I have to change the number of xattrs reserved by 
Smack in patch 3.

Thanks

Roberto