linux-kernel - Re: [PATCH v3 1/4] mm/mlock: return EINVAL if len overflows for mlock/munlock

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Date:   Fri, 3 Feb 2023 18:14:29 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wupeng Ma <mawupeng1@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kuleshovmail@...il.com, aneesh.kumar@...ux.ibm.com
Subject: Re: [PATCH v3 1/4] mm/mlock: return EINVAL if len overflows for
 mlock/munlock

On 28.01.23 07:32, Wupeng Ma wrote:
> From: Ma Wupeng <mawupeng1@...wei.com>
> 
> While testing mlock, we have a problem if the len of mlock is ULONG_MAX.
> The return value of mlock is zero. But nothing will be locked since the
> len in do_mlock overflows to zero due to the following code in mlock:
> 
>    len = PAGE_ALIGN(len + (offset_in_page(start)));
> 
> The same problem happens in munlock.
> 
> Add new check and return -EINVAL to fix this overflowing scenarios since
> they are absolutely wrong.
> 
> Return 0 early to avoid burn a bunch of cpu cycles if len == 0.
> 
> Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
> ---
>   mm/mlock.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 7032f6dd0ce1..eb09968ba27f 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -478,8 +478,6 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
>   	end = start + len;
>   	if (end < start)
>   		return -EINVAL;
> -	if (end == start)
> -		return 0;
>   	vma = mas_walk(&mas);
>   	if (!vma)
>   		return -ENOMEM;
> @@ -575,7 +573,13 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
>   	if (!can_do_mlock())
>   		return -EPERM;
>   
> +	if (!len)
> +		return 0;
> +
>   	len = PAGE_ALIGN(len + (offset_in_page(start)));
> +	if (!len)
> +		return -EINVAL;
> +
>   	start &= PAGE_MASK;

The "ordinary" overflows are detected in apply_vma_lock_flags(), correct?

-- 
Thanks,

David / dhildenb