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

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Message-ID: <eb1efdee-6d9c-2f03-fb88-ffec0db61037@suse.cz>
Date:   Tue, 12 May 2020 11:21:59 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Vasily Averin <vvs@...tuozzo.com>,
        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 08. 05. 20, 12:01, Vasily Averin wrote:
> 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.

Any progress on this? 5.7-rc*, 5.4.40, and 5.6.12 are still affected.

Wouldn't it be better to rebase (apply the originally submitted patch)
before the XA rewrite and push that one to Linus?

thanks,
-- 
js
suse labs