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Message-ID: <a5ae7d0c-61dc-3071-434d-5152c46c05e8@huawei.com>
Date: Mon, 6 Feb 2023 08:48:05 +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 2023/2/4 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().
do_mlock
apply_vma_lock_flags
end = start + len;
if (end == start)
return 0;
Move the checking to the begin is easier to detect overflows and make the logic clearer
and avoid burn a bunch of cpu cycles.
>
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