linux-kernel - Re: [PATCH v4 2/5] security: Rewrite security_old_inode_init

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Date:   Mon, 21 Nov 2022 15:54:19 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>,
        dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, stephen.smalley.work@...il.com,
        eparis@...isplace.org, casey@...aufler-ca.com
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, nicolas.bouchinet@...p-os.org,
        Roberto Sassu <roberto.sassu@...wei.com>,
        ocfs2-devel@....oracle.com
Subject: Re: [PATCH v4 2/5] security: Rewrite
 security_old_inode_init_security()

On Mon, 2022-11-21 at 10:45 +0100, Roberto Sassu wrote:
> > As ocfs2 already defines initxattrs, that leaves only reiserfs missing
> > initxattrs().  A better, cleaner solution would be to define one.
> 
> If I understood why security_old_inode_init_security() is called
> instead of security_inode_init_security(), the reason seems that the
> filesystem code uses the length of the obtained xattr to make some
> calculations (e.g. reserve space). The xattr is written at a later
> time.
> 
> Since for reiserfs there is a plan to deprecate it, it probably
> wouldn't be worth to support the creation of multiple xattrs. I would
> define a callback to take the first xattr and make a copy, so that
> calling security_inode_init_security() + reiserfs_initxattrs() is
> equivalent to calling security_old_inode_init_security().
> 
> But then, this is what anyway I was doing with the
> security_initxattrs() callback, for all callers of security_old_inode_i
> nit_security().
> 
> Also, security_old_inode_init_security() is exported to kernel modules.
> Maybe, it is used somewhere. So, unless we plan to remove it
> completely, it should be probably be fixed to avoid multiple LSMs
> successfully setting an xattr, and losing the memory of all except the
> last (which this patch fixes by calling security_inode_init_security())
> .
> 
> If there is still the preference, I will implement the reiserfs
> callback and make a fix for security_old_inode_init_security().

There's no sense in doing both, as the purpose of defining a reiserfs
initxattrs function was to clean up this code making it more readable.

Mimi