[PATCH V2] fs: export anon_inode_make_secure_inode() and fix secretmem LSM bypass

[Shivank Garg]

On 6/23/2025 7:21 PM, David Hildenbrand wrote:
> 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 at redhat.com>
>> Suggested-by: Mike Rapoport <rppt at kernel.org>
>> Signed-off-by: Shivank Garg <shivankg at amd.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 ...
> 
I agree. I did not think about backporting conflicts when sending the patch.

Christian, I can send it as 2 separate patches to make it easier?

Thanks,
Shivank