linux-kernel - Re: [PATCH v2] memfd,selinux: call security_inode_init_security

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Message-ID: <CA+zpnLdbLjuGrk-178coxAH1pzpEA1jRzGn8zU9DHZ1rQspP4A@mail.gmail.com>
Date: Tue, 9 Sep 2025 08:51:12 +1000
From: Thiébaud Weksteen <tweek@...gle.com>
To: Stephen Smalley <stephen.smalley.work@...il.com>
Cc: Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>, 
	Hugh Dickins <hughd@...gle.com>, Jeff Vander Stoep <jeffv@...gle.com>, Nick Kralevich <nnk@...gle.com>, 
	Jeff Xu <jeffxu@...gle.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Isaac Manjarres <isaacmanjarres@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-security-module@...r.kernel.org, selinux@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v2] memfd,selinux: call security_inode_init_security_anon

On Tue, Sep 9, 2025 at 2:27 AM Stephen Smalley
<stephen.smalley.work@...il.com> wrote:
>
> On Sun, Sep 7, 2025 at 9:34 PM Thiébaud Weksteen <tweek@...gle.com> wrote:
> >
> > Prior to this change, no security hooks were called at the creation of a
> > memfd file. It means that, for SELinux as an example, it will receive
> > the default type of the filesystem that backs the in-memory inode. In
> > most cases, that would be tmpfs, but if MFD_HUGETLB is passed, it will
> > be hugetlbfs. Both can be considered implementation details of memfd.
> >
> > It also means that it is not possible to differentiate between a file
> > coming from memfd_create and a file coming from a standard tmpfs mount
> > point.
> >
> > Additionally, no permission is validated at creation, which differs from
> > the similar memfd_secret syscall.
> >
> > Call security_inode_init_security_anon during creation. This ensures
> > that the file is setup similarly to other anonymous inodes. On SELinux,
> > it means that the file will receive the security context of its task.
> >
> > The ability to limit fexecve on memfd has been of interest to avoid
> > potential pitfalls where /proc/self/exe or similar would be executed
> > [1][2]. Reuse the "execute_no_trans" and "entrypoint" access vectors,
> > similarly to the file class. These access vectors may not make sense for
> > the existing "anon_inode" class. Therefore, define and assign a new
> > class "memfd_file" to support such access vectors.
> >
> > Guard these changes behind a new policy capability named "memfd_class".
> >
> > [1] https://crbug.com/1305267
> > [2] https://lore.kernel.org/lkml/20221215001205.51969-1-jeffxu@google.com/
> >
> > Signed-off-by: Thiébaud Weksteen <tweek@...gle.com>
> > Acked-by: Stephen Smalley <stephen.smalley.work@...il.com>
> > Tested-by: Stephen Smalley <stephen.smalley.work@...il.com>
>
> When you revise a patch, you aren't supposed to retain other's tags
> since they haven't technically reviewed, agreed to, or tested the
> revised change.
> That said, I have now done so and thus these tags can remain!
>

I'm sorry for that. Thanks for the clarification, I wasn't sure what
the process was. And thanks for the review!