linux-kernel - Re: [PATCH] ipc/util.c: sysvipc_find_ipc() incorrectly updates position index

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Date:   Fri, 8 May 2020 13:01:38 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>,
        Andreas Schwab <schwab@...e.de>
Subject: Re: [PATCH] ipc/util.c: sysvipc_find_ipc() incorrectly updates
 position index

On 5/8/20 9:07 AM, Vasily Averin wrote:
> On 5/8/20 6:36 AM, Matthew Wilcox wrote:
>> On Thu, May 07, 2020 at 05:02:42PM -0700, Andrew Morton wrote:
>>> Here's how I resolved things.  Please check?
>>>
>>> static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
>>> 					      loff_t *new_pos)
>>> {
>>> 	unsigned long index = pos;
>>> 	struct kern_ipc_perm *ipc;
>>>
>>> 	rcu_read_lock();
>>> 	ipc = xa_find(&ids->ipcs, &index, ULONG_MAX, XA_PRESENT);
>>> 	if (ipc)
>>> 		ipc_lock_object(ipc);
>>> 	else
>>> 		rcu_read_unlock();
>>> 	*new_pos = pos + 1;
>>> 	return ipc;
>>> }
>>
>> Surely that should be '*new_pos = index + 1'?  Or did I misunderstand
>> the reasoning behind the other patch?
> 
> I'm not sure however it looks like xa_find() can return index < pos
it seems, I was wrong here.
So I'm agree with Matthew, '*new_pos = index + 1' should be used.

Thank you,
	Vasily Averin