[PATCH 2/2] mm: memfd_luo: preserve file seals

[Pratyush Yadav]

Hi Jason,

On Mon, Jan 26 2026, Jason Gunthorpe wrote:

> On Sun, Jan 25, 2026 at 02:03:29PM +0200, Mike Rapoport wrote:
>> > @@ -67,11 +72,13 @@ struct memfd_luo_folio_ser {
>> >  struct memfd_luo_ser {
>> >  	u64 pos;
>> >  	u64 size;
>> > +	u64 seals:8;
>> 
>> Kernel uABI defines seals as unsigned int, I think we can spare u32 for
>> them and reserve a u32 flags for other memfd flags (MFD_CLOEXEC,
>> MFD_HUGETLB etc).
>
> It is a bit worse than that, the "v2" version is only going to support
> some set of seals (probably the set defined in v6.19) and if there are
> new seals down the road then this needs a version bump.

If we are running say kernel X, then X + 1 will always support a
superset of the seals, since the seals are UAPI. So it should be able to
handle all the seals that are given to it by X. This only becomes a
problem on rollbacks. Is this what you are worried about or am I missing
something?

>
> So I'd check that only supported seals are set here:
>
>> > +     seals = memfd_get_seals(args->file);
>> > +     if (seals < 0) {
>> > +             err = seals;
>> > +             goto err_free_ser;
>> > +     }
>> > +
>> >       ser->pos = args->file->f_pos;
>> >       ser->size = i_size_read(inode);
>> > +     ser->seals = seals;
>
> ..
>
>> > @@ -444,13 +453,23 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
>> >  	if (!ser)
>> >  		return -EINVAL;
>> >  
>> > -	file = memfd_alloc_file("", 0);
>> > +	/*
>> > +	 * The seals are preserved. Allow sealing here so they can be added
>> > +	 * later.
>> > +	 */
>> > +	file = memfd_alloc_file("", MFD_ALLOW_SEALING);
>> >  	if (IS_ERR(file)) {
>> >  		pr_err("failed to setup file: %pe\n", file);
>> >  		err = PTR_ERR(file);
>> >  		goto free_ser;
>> >  	}
>> >  
>> > +	err = memfd_add_seals(file, ser->seals);
>
> Because we really don't want this to fail :\
>
> Jason

-- 
Regards,
Pratyush Yadav