Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] ipc/util.c: sysvipc_find_ipc() incorrectly updates
 position index
From:   Vasily Averin <vvs@virtuozzo.com>
To:     Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, Waiman Long <longman@redhat.com>,
        Andreas Schwab <schwab@suse.de>
References: <ad24ee52-21a8-3ff0-e968-63d315472b91@virtuozzo.com>
 <4921fe9b-9385-a2b4-1dc4-1099be6d2e39@virtuozzo.com>
 <20200507170242.6cbb88ae672deed67152e221@linux-foundation.org>
 <20200508033625.GO16070@bombadil.infradead.org>
 <e25e5a42-159c-6bad-4f14-d70461a78b72@virtuozzo.com>
Message-ID: <c89b587a-b570-2a11-3001-d1c8444f3a2f@virtuozzo.com>
Date:   Fri, 8 May 2020 13:01:38 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
In-Reply-To: <e25e5a42-159c-6bad-4f14-d70461a78b72@virtuozzo.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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