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From:   Lokesh Gidra <lokeshgidra@google.com>
Date:   Mon, 17 Aug 2020 14:10:20 -0700
Message-ID: <CA+EESO5kDbSCcpzxij6M0aWXqKDyFds+azksQFrXES6ACzTFtA@mail.gmail.com>
Subject: Re: [PATCH v6 1/3] Add a new LSM-supporting anonymous inode interface
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     James Morris <jmorris@namei.org>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Eric Biggers <ebiggers@kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Paul Moore <paul@paul-moore.com>,
        Eric Paris <eparis@parisplace.org>,
        Daniel Colascione <dancol@dancol.org>,
        Kees Cook <keescook@chromium.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        KP Singh <kpsingh@google.com>,
        David Howells <dhowells@redhat.com>,
        Thomas Cedeno <thomascedeno@google.com>,
        Anders Roxell <anders.roxell@linaro.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Matthew Garrett <matthewgarrett@google.com>,
        Aaron Goidel <acgoide@tycho.nsa.gov>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        YueHaibing <yuehaibing@huawei.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        Adrian Reber <areber@redhat.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        SElinux list <selinux@vger.kernel.org>,
        Kalesh Singh <kaleshsingh@google.com>,
        Calin Juravle <calin@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Nick Kralevich <nnk@google.com>,
        Jeffrey Vander Stoep <jeffv@google.com>,
        kernel-team@android.com, Daniel Colascione <dancol@google.com>
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On Fri, Aug 7, 2020 at 4:02 PM Al Viro <viro@zeniv.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 =E2=80=98logical child=E2=80=99 b=
ecause the
context_inode (userfaultfd inode of the parent process) provides the
security context required for creation of child process=E2=80=99 userfaultf=
d
inode. But there is no relationship beyond this point. Therefore, no
reference to context_inode is held anywhere.