linux-kernel - Re: [PATCH] fs: export anon_inode_make_secure

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Message-ID: <aFPuAi8tPcmsbTF4@kernel.org>
Date: Thu, 19 Jun 2025 14:01:22 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Christian Brauner <brauner@...nel.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, Shivank Garg <shivankg@....com>,
	david@...hat.com, akpm@...ux-foundation.org, paul@...l-moore.com,
	viro@...iv.linux.org.uk, seanjc@...gle.com, willy@...radead.org,
	pbonzini@...hat.com, tabba@...gle.com, afranji@...gle.com,
	ackerleytng@...gle.com, jack@...e.cz, hch@...radead.org,
	cgzones@...glemail.com, ira.weiny@...el.com, roypat@...zon.co.uk,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] fs: export anon_inode_make_secure_inode() and fix
 secretmem LSM bypass

On Thu, Jun 19, 2025 at 12:38:25PM +0200, Christian Brauner wrote:
> On Thu, Jun 19, 2025 at 11:13:49AM +0200, Vlastimil Babka wrote:
> > On 6/19/25 09:31, Shivank Garg wrote:
> > > Export anon_inode_make_secure_inode() to allow KVM guest_memfd to create
> > > anonymous inodes with proper security context. This replaces the current
> > > pattern of calling alloc_anon_inode() followed by
> > > inode_init_security_anon() for creating security context manually.
> > > 
> > > This change also fixes a security regression in secretmem where the
> > > S_PRIVATE flag was not cleared after alloc_anon_inode(), causing
> > > LSM/SELinux checks to be bypassed for secretmem file descriptors.
> > > 
> > > As guest_memfd currently resides in the KVM module, we need to export this
> > 
> > Could we use the new EXPORT_SYMBOL_GPL_FOR_MODULES() thingy to make this
> > explicit for KVM?
> 
> Oh? Enlighten me about that, if you have a second, please. 

>From Documentation/core-api/symbol-namespaces.rst:

The macro takes a comma separated list of module names, allowing only those
modules to access this symbol. Simple tail-globs are supported.

For example::

  EXPORT_SYMBOL_GPL_FOR_MODULES(preempt_notifier_inc, "kvm,kvm-*")

will limit usage of this symbol to modules whoes name matches the given
patterns.


-- 
Sincerely yours,
Mike.