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

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Message-ID: <d13ea810-e9a8-2741-11ce-5e20f1ba0334@redhat.com>
Date:   Mon, 2 Jan 2023 14:22:26 +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,
        clameter@....com
Subject: Re: [PATCH 0/4] return EINVAL for illegal user memory range

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?


-- 
Thanks,

David / dhildenb