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

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Date:   Mon, 6 Feb 2023 18:05:01 +0100
From:   David Hildenbrand <david@...hat.com>
To:     mawupeng <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 06.02.23 01:48, mawupeng wrote:
> 
> 
> On 2023/2/4 1:14, David Hildenbrand wrote:
>> 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?
> 
> Overflow is not checked anywhere however the ordinary return early if len == 0 is detected in apply_vma_lock_flags().
> 

I meant the

end = start + len;
if (end < start)
	return -EINVAL;

Essentially, what I wanted to double-check is that with your changes, we 
catch all kinds of overflows as documented in the man page, correct?

-- 
Thanks,

David / dhildenb