linux-kernel - Re: [PATCH v9 1/3] Add a new LSM-supporting anonymous inode interface

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Message-ID: <20201009044519.GC854@sol.localdomain>
Date:   Thu, 8 Oct 2020 21:45:19 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Lokesh Gidra <lokeshgidra@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        James Morris <jmorris@...ei.org>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>,
        Daniel Colascione <dancol@...col.org>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        KP Singh <kpsingh@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Thomas Cedeno <thomascedeno@...gle.com>,
        Anders Roxell <anders.roxell@...aro.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Matthew Garrett <matthewgarrett@...gle.com>,
        Aaron Goidel <acgoide@...ho.nsa.gov>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        YueHaibing <yuehaibing@...wei.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Adrian Reber <areber@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        kaleshsingh@...gle.com, calin@...gle.com, surenb@...gle.com,
        nnk@...gle.com, jeffv@...gle.com, kernel-team@...roid.com,
        Daniel Colascione <dancol@...gle.com>
Subject: Re: [PATCH v9 1/3] Add a new LSM-supporting anonymous inode interface

On Wed, Sep 23, 2020 at 12:33:22PM -0700, Lokesh Gidra wrote:
> +static struct file *_anon_inode_getfile(const char *name,
> +					const struct file_operations *fops,
> +					void *priv, int flags,
> +					const struct inode *context_inode,
> +					bool secure)
> +{

Nit: in Linux kernel code, using double underscore function prefixes is much
more common than single underscores.

> +/**
> + * Like anon_inode_getfd(), but adds the @context_inode argument to
> + * allow security modules to control creation of the new file. Once the
> + * security module makes the decision, this inode is no longer needed
> + * and hence reference to it is not held.
> + */
> +int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
> +			    void *priv, int flags,
> +			    const struct inode *context_inode)
> +{
> +	return _anon_inode_getfd(name, fops, priv, flags, context_inode, true);
> +}
> +EXPORT_SYMBOL_GPL(anon_inode_getfd_secure);

This new function has two callers, one of which passes context_inode=NULL.

But from the comment, it sounds like the purpose of this function is just to add
the context_inode argument.  So one would expect anon_inode_getfd() to be
equivalent to anon_inode_getfd_secure(..., NULL).

Apparently, that's not actually the case though.  Can you fix the comment to
describe what the function actually does?

- Eric