Re: [PATCH] mm/memfd_luo: validate serialized_data before conversion

[tarunsahu]

Mike Rapoport <rppt@xxxxxxxxxx> writes:

> On Thu, Jun 11, 2026 at 06:11:13PM +0000, Pasha Tatashin wrote:
>> On 06-11 17:28, Mike Rapoport wrote:
>> > On Thu, Jun 11, 2026 at 03:37:12PM +0200, Pratyush Yadav wrote:
>> > > On Thu, Jun 11 2026, Mike Rapoport wrote:
>> > > 
>> > > > On Thu, Jun 11, 2026 at 10:30:03AM +0000, Tarun Sahu wrote:
>> > > >> In memfd_luo_finish() and memfd_luo_retrieve(), phys_to_virt() was called
>> > > >> on args->serialized_data before checking if the physical address is valid.
>> > > >> Since physical address 0 does not map to virtual NULL (due to direct
>> > > >> mapping offsets), the subsequent check 'if (!ser)' was ineffective at
>> > > >> catching a missing serialized_data, leading to unsafe dereferences later.
>> > > >> 
>> > > >> Validate that args->serialized_data is non-zero before calling
>> > > >> phys_to_virt().
>> > > >> 
>> > > >> Fixes: b3749f174d68 ("mm: memfd_luo: allow preserving memfd")
>> > > >> Signed-off-by: Tarun Sahu <tarunsahu@xxxxxxxxxx>
>> > > >> ---
>> > > >>  mm/memfd_luo.c | 10 ++++++----
>> > > >>  1 file changed, 6 insertions(+), 4 deletions(-)
>> > > >> 
>> > > >> diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
>> > > >> index 59de210bee5f..10f3983b0060 100644
>> > > >> --- a/mm/memfd_luo.c
>> > > >> +++ b/mm/memfd_luo.c
>> > > >> @@ -397,10 +397,11 @@ static void memfd_luo_finish(struct liveupdate_file_op_args *args)
>> > > >>  	if (args->retrieve_status)
>> > > >>  		return;
>> > > >>  
>> > > >> -	ser = phys_to_virt(args->serialized_data);
>> > > >> -	if (!ser)
>> > > >> +	if (!args->serialized_data)
>> > > >
>> > > > We really should make args->serialized_data a KHOSER_PTR
>> > > 
>> > > Hmm, that would also be a good idea. I suppose then it would be a better
>> > > to directly convert to using KHOSER_PTR() instead of this patch?
>> > 
>> > Makes sense.
>> 
>> I think we should systematically cover all  phys_to_virt  conversions 
>> and add  KOSHER_PTR() , instead of an ad-hoc approach of adding it as we 
>> go. So, let's take this patch and do a series where we properly convert 
>> everything and provide guidance for others to use going forward.
>
> It's too late for this patch for -rc1. So let's systematically convert all
> 4 or 5 direct phys_to_virt() conversions in the next cycle and be done with
> it.
>
> We have enough time to make it by -rc2.

I am already working on converitng them to use KHOSER_PTR. I have patch
ready, Will send soon after some testing.

~Tarun

>  
>> Pasha
>
> -- 
> Sincerely yours,
> Mike.