linux-kernel - Re: [PATCH V2] fs: export anon_inode_make_secure

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Message-ID: <f2a205a5-aca9-4788-88ff-bfb3283610c5@redhat.com>
Date: Mon, 23 Jun 2025 15:51:28 +0200
From: David Hildenbrand <david@...hat.com>
To: Shivank Garg <shivankg@....com>, akpm@...ux-foundation.org,
 brauner@...nel.org, paul@...l-moore.com, rppt@...nel.org,
 viro@...iv.linux.org.uk
Cc: seanjc@...gle.com, vbabka@...e.cz, 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 V2] fs: export anon_inode_make_secure_inode() and fix
 secretmem LSM bypass

On 20.06.25 09:03, 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
> symbol for use outside the core kernel. In the future, guest_memfd might be
> moved to core-mm, at which point the symbols no longer would have to be
> exported. When/if that happens is still unclear.
> 
> Fixes: 2bfe15c52612 ("mm: create security context for memfd_secret inodes")
> Suggested-by: David Hildenbrand <david@...hat.com>
> Suggested-by: Mike Rapoport <rppt@...nel.org>
> Signed-off-by: Shivank Garg <shivankg@....com>


In general, LGTM, but I think the actual fix should be separated from 
exporting it for guest_memfd purposes?

Also makes backporting easier, when EXPORT_SYMBOL_GPL_FOR_MODULES does 
not exist yet ...

Leaving deciding about that to fs people.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb