linux-kernel - Re: [RFC PATCH] mm: create security context for memfd

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Message-ID: <CAJ2a_DeAUcGTGm_fk8viVbeFXr6FLrJ-oLw-abwFND6Kv0u0gQ@mail.gmail.com>
Date:   Thu, 17 Feb 2022 15:24:42 +0100
From:   Christian Göttsche <cgzones@...glemail.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     SElinux list <selinux@...r.kernel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: create security context for memfd_secret inodes

On Thu, 27 Jan 2022 at 00:01, Paul Moore <paul@...l-moore.com> wrote:
>
> On Tue, Jan 25, 2022 at 9:33 AM Christian Göttsche
> <cgzones@...glemail.com> wrote:
> >
> > Create a security context for the inodes created by memfd_secret(2) via
> > the LSM hook inode_init_security_anon to allow a fine grained control.
> > As secret memory areas can affect hibernation and have a global shared
> > limit access control might be desirable.
> >
> > Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> > ---
> > An alternative way of checking memfd_secret(2) is to create a new LSM
> > hook and e.g. for SELinux check via a new process class permission.
> > ---
> >  mm/secretmem.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
>
> This seems reasonable to me, and I like the idea of labeling the anon
> inode as opposed to creating a new set of LSM hooks.  If we want to
> apply access control policy to the memfd_secret() fds we are going to
> need to attach some sort of LSM state to the inode, we might as well
> use the mechanism we already have instead of inventing another one.

Any further comments (on design or implementation)?

Should I resend a non-rfc?

One naming question:
Should the anonymous inode class be named "[secretmem]", like
"[userfaultfd]", or "[secret_mem]" similar to "[io_uring]"?


> > diff --git a/mm/secretmem.c b/mm/secretmem.c
> > index 22b310adb53d..b61cd2f661bc 100644
> > --- a/mm/secretmem.c
> > +++ b/mm/secretmem.c
> > @@ -164,11 +164,20 @@ static struct file *secretmem_file_create(unsigned long flags)
> >  {
> >         struct file *file = ERR_PTR(-ENOMEM);
> >         struct inode *inode;
> > +       const char *anon_name = "[secretmem]";
> > +       const struct qstr qname = QSTR_INIT(anon_name, strlen(anon_name));
> > +       int err;
> >
> >         inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
> >         if (IS_ERR(inode))
> >                 return ERR_CAST(inode);
> >
> > +       err = security_inode_init_security_anon(inode, &qname, NULL);
> > +       if (err) {
> > +               file = ERR_PTR(err);
> > +               goto err_free_inode;
> > +       }
> > +
> >         file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
> >                                  O_RDWR, &secretmem_fops);
> >         if (IS_ERR(file))
> > --
> > 2.34.1
>
> --
> paul-moore.com