Re: [PATCH 04/16] mm/shmem: honour F_SEAL_EXEC when an ACL is set

[Kiryl Shutsemau]

On Mon, Oct 26, 2026 at 10:40:37AM +0100, David Hildenbrand (Arm) wrote:
> From: Chris Mason <mason@xxxxxxxxxx>
> 
> The owner of a memfd sealed with F_SEAL_EXEC can still change its
> execute bits by setting a POSIX access ACL. With CONFIG_TMPFS_POSIX_ACL,
> this lets an unprivileged owner make a non-executable memfd executable,
> bypassing vm.memfd_noexec=2.
> 
> simple_set_acl() updates i_mode directly, bypassing the seal check in
> shmem_setattr(). Add shmem_set_acl() to check the resulting mode. Share
> the F_SEAL_EXEC check with shmem_setattr() using memfd_check_seals_mode()
> in include/linux/memfd.h.
> 
> Fix generated by an LLM and sent by Chris Mason in private.
> 
> Fixes: 6fd7353829ca ("mm/memfd: add F_SEAL_EXEC")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Chris Mason <mason@xxxxxxxxxx>
> [ david: use common helper; simplify description ]
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Acked-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov