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

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Message-ID: <c74516a1-9f9d-6c5f-0dc5-7ea07c975dfb@huawei.com>
Date:   Tue, 7 Feb 2023 09:24:19 +0800
From:   mawupeng <mawupeng1@...wei.com>
To:     <david@...hat.com>, <akpm@...ux-foundation.org>
CC:     <mawupeng1@...wei.com>, <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 2023/2/7 1:05, David Hildenbrand wrote:
> 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?

Oh i see. You are right, The "ordinary" overflows are detected for mlock/munlock in apply_vma_lock_flags().

Yes, we may need to update the man page for all these four syscalls.

Thanks, 

mawupeng.


>