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

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On 06-11 10:30, 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@google.com>

Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com> 

> ---
>  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)
>  		return;
>  
> +	ser = phys_to_virt(args->serialized_data);
> +
>  	if (ser->nr_folios) {
>  		folios_ser = kho_restore_vmalloc(&ser->folios);
>  		if (!folios_ser)
> @@ -522,10 +523,11 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
>  	struct file *file;
>  	int err;
>  
> -	ser = phys_to_virt(args->serialized_data);
> -	if (!ser)
> +	if (!args->serialized_data)
>  		return -EINVAL;
>  
> +	ser = phys_to_virt(args->serialized_data);
> +
>  	/* Make sure the file only has seals supported by this version. */
>  	if (ser->seals & ~MEMFD_LUO_ALL_SEALS) {
>  		err = -EOPNOTSUPP;
> 
> base-commit: 9716c086c8e8b141d35aa61f2e96a2e83de212a7
> -- 
> 2.54.0.1099.g489fc7bff1-goog
>