linux-kernel - Re: [PATCH v17 05/10] fs,landlock: Support filesystem access-control

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Date:   Thu, 14 May 2020 12:39:58 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     James Morris <jmorris@...ei.org>,
        Casey Schaufler <casey@...aufler-ca.com>
Cc:     linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...capital.net>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Mickaël Salaün <mickael.salaun@....gouv.fr>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-security-module@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v17 05/10] fs,landlock: Support filesystem access-control


On 14/05/2020 05:37, James Morris wrote:
> On Mon, 11 May 2020, Mickaël Salaün wrote:
> 
> 
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 45cc10cdf6dd..2276642f8e05 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -1517,6 +1517,11 @@ struct super_block {
>>  	/* Pending fsnotify inode refs */
>>  	atomic_long_t s_fsnotify_inode_refs;
>>  
>> +#ifdef CONFIG_SECURITY_LANDLOCK
>> +	/* References to Landlock underlying objects */
>> +	atomic_long_t s_landlock_inode_refs;
>> +#endif
>> +
> 
> This needs to be converted to the LSM API via superblock blob stacking.
> 
> See Casey's old patch: 
> https://lore.kernel.org/linux-security-module/20190829232935.7099-2-casey@schaufler-ca.com/

s_landlock_inode_refs is quite similar to s_fsnotify_inode_refs, but I
can do it once the superblock security blob patch is upstream. Is it a
blocker for now? What is the current status of lbs_superblock?

Anyway, we also need to have a call to landlock_release_inodes() in
generic_shutdown_super(), which does not fit the LSM framework, and I
think it is not an issue. Landlock handling of inodes is quite similar
to fsnotify.