Re: [PATCH] mm/nommu: Reject wrapping ranges in access_remote_vm()

[Andrew Morton]

On Wed,  9 Sep 2026 09:42:31 +0300 Anastasios Papagiannis <tasos.papagiannnis@xxxxxxxxx> wrote:

> The NOMMU implementation of access_process_vm() rejects address ranges
> whose end wraps around, but access_remote_vm() bypasses this check even
> though both functions delegate to __access_remote_vm().
> 
> Move the wraparound check into __access_remote_vm() so it applies to
> both entry points.

lgtm, thanks.

> This is originally reported in [1].
> 
> [1] https://lore.kernel.org/bpf/4ef240a5bea36ff84df9589671367832860795159386a4c8fba546a0fa8b786f@xxxxxxxxxxxxxxx/

Ah, bpfbot scored one.

Sashiko might have found more issues in there:
	https://sashiko.dev/#/patchset/20260909064231.18693-1-tasos.papagiannnis@xxxxxxxxx

I'll optimistically cc Hajime Tazaki, who has been doing some NOMMU
work recently.

> Fixes: f55f199b7d76 ("NOMMU: implement access_remote_vm")
> Signed-off-by: Anastasios Papagiannis <tasos.papagiannnis@xxxxxxxxx>
> ---
>  mm/nommu.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 498e01ee40b0..ed44510e3770 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1674,6 +1674,9 @@ static int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
>  	struct vm_area_struct *vma;
>  	int write = gup_flags & FOLL_WRITE;
>  
> +	if (addr + len < addr)
> +		return 0;
> +
>  	if (mmap_read_lock_killable(mm))
>  		return 0;
>  
> @@ -1727,9 +1730,6 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
>  {
>  	struct mm_struct *mm;
>  
> -	if (addr + len < addr)
> -		return 0;
> -
>  	mm = get_task_mm(tsk);
>  	if (!mm)
>  		return 0;
>