linux-kernel - Re: [PATCH v3 09/16] SELinux: Abstract use of file security blob

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Message-ID: <4db0c110-c1aa-aac8-901f-a9abf662b605@schaufler-ca.com>
Date:   Thu, 20 Sep 2018 08:20:50 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     David Laight <David.Laight@...LAB.COM>,
        LSM <linux-security-module@...r.kernel.org>,
        James Morris <jmorris@...ei.org>,
        SE Linux <selinux@...ho.nsa.gov>,
        LKLM <linux-kernel@...r.kernel.org>,
        John Johansen <john.johansen@...onical.com>,
        Kees Cook <keescook@...omium.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Mickaël Salaün <mic@...ikod.net>,
        Salvatore Mesoraca <s.mesoraca16@...il.com>
Subject: Re: [PATCH v3 09/16] SELinux: Abstract use of file security blob

On 9/20/2018 1:51 AM, David Laight wrote:
> From: Casey Schaufler
>> Sent: 20 September 2018 01:21
>>
>> SELinux: Abstract use of file security blob
>>
>> Don't use the file->f_security pointer directly.
>> Provide a helper function that provides the security blob pointer.
> ...
>> +static inline struct file_security_struct *selinux_file(const struct file *file)
>> +{
>> +	return file->f_security;
>> +}
>> +
> Why?

In patch 16/16 this becomes:

 static inline struct file_security_struct *selinux_file(const struct file *file)
 {
+#ifdef CONFIG_SECURITY_STACKING
+	return file->f_security + selinux_blob_sizes.lbs_file;
+#else
 	return file->f_security;
+#endif
 }

You could hard code this bit everywhere it's used, but that
would be prone to error. I'm not generally an abstractionist
myself, but it these cases abstraction adds value.