linux-kernel - Re: [PATCH 0/4] return EINVAL for illegal user memory range

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Date:   Wed, 4 Jan 2023 17:32:30 +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 0/4] return EINVAL for illegal user memory range



On 2023/1/2 21:22, David Hildenbrand wrote:
> On 05.12.22 04:41, 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)));
>>
>> However this problem appear in multiple syscalls.
>>
>> Since TASK_SIZE is the maximum user space address. The start or len of
>> mlock shouldn't be bigger than this. Function access_ok can be used to
>> check this issue, so return -EINVAL if bigger.
> 
> I assume this makes sure that what we document holds:
> 
> EINVAL (mlock(),  mlock2(),  and  munlock()) The result of the addition
>     addr+len was less than addr (e.g., the addition may have
>     resulted in an overflow).
> 
> So instead of adding access_ok() checks, wouldn't be the right think to do checking for overflows?

I agree with you. Do checking only for overflows do seems nice since we need to keep
backward-compatibility.

> 
>