Re: [PATCH] kernel/sys.c: fix prctl_set_auxv to use sizeof instead of user-supplied len

[David Laight <david.laight.linux@gmail.com>]

On Mon,  1 Jun 2026 22:40:02 -0400
Aiden Bowling <aidenlbowling56@gmail.com> wrote:

> prctl_set_auxv() passed the user-supplied 'len' to memcpy() when copying
> into mm->saved_auxv, instead of sizeof(user_auxv). Since user_auxv is
> already sized to the full auxv buffer, using 'len' risks a partial write
> if the caller supplies a smaller value. Use sizeof(user_auxv) to always
> copy the full buffer after validation.

Is it possibly that the caller only wants to write the first few values?

-- David

> 
> Signed-off-by: Aiden Bowling <aidenlbowling56@gmail.com>
> ---
>  kernel/sys.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 62e842055cc9..d3f5229649e3 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2189,7 +2189,7 @@ static int prctl_set_auxv(struct mm_struct *mm, unsigned long addr,
>  	BUILD_BUG_ON(sizeof(user_auxv) != sizeof(mm->saved_auxv));
>  
>  	task_lock(current);
> -	memcpy(mm->saved_auxv, user_auxv, len);
> +	memcpy(mm->saved_auxv, user_auxv, sizeof(user_auxv));
>  	task_unlock(current);
>  
>  	return 0;
> 
> base-commit: e43ffb69e0438cddd72aaa30898b4dc446f664f8