linux-kernel - Re: [PATCH v6 1/3] Add a new LSM-supporting anonymous inode interface

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Date:   Mon, 17 Aug 2020 14:10:20 -0700
From:   Lokesh Gidra <lokeshgidra@...gle.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     James Morris <jmorris@...ei.org>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Eric Biggers <ebiggers@...nel.org>,
        "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 FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        SElinux list <selinux@...r.kernel.org>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Calin Juravle <calin@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Nick Kralevich <nnk@...gle.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        kernel-team@...roid.com, Daniel Colascione <dancol@...gle.com>
Subject: Re: [PATCH v6 1/3] Add a new LSM-supporting anonymous inode interface

On Fri, Aug 7, 2020 at 4:02 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Fri, Aug 07, 2020 at 03:49:39PM -0700, Lokesh Gidra wrote:
>
> > The new functions accept an optional context_inode parameter that
> > callers can use to provide additional contextual information to
> > security modules, e.g., indicating that one anonymous struct file is a
> > logical child of another, allowing a security model to propagate
> > security information from one to the other.
>
> What the hell is "logical child" and what are the lifetime rules implied
> by that relationship?

context_inode provides the security context required by the security
modules for granting/denying permission to create an anon inode of the
same type.

In case of userfaultfd, the relationship between the context_inode and
the created inode is described as that of ‘logical child’ because the
context_inode (userfaultfd inode of the parent process) provides the
security context required for creation of child process’ userfaultfd
inode. But there is no relationship beyond this point. Therefore, no
reference to context_inode is held anywhere.