linux-kernel - Re: [PATCH 1/8] idr: fix overflow bug for the max-high layer

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Date:	Sat, 19 Apr 2014 01:08:46 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jean Delvare <jdelvare@...e.de>,
	Monam Agarwal <monamagarwal123@...il.com>,
	Jeff Layton <jlayton@...hat.com>,
	Andreas Gruenbacher <agruen@...bit.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH 1/8] idr: fix overflow bug for the max-high layer

On Sat, Apr 19, 2014 at 12:29 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,

Hi,

Should I resend the patch with your updated changelog?
Or something else I need to do?

>
> Subject: idr: fix overflow bug during maximum ID calculation at maximum height
>
> On Fri, Apr 18, 2014 at 08:49:48PM +0800, Lai Jiangshan wrote:
>> In idr_replace(), when the top layer is the max-high layer(p->layer == 3),
>> The "(1 << n)" will overflow and the result is 0, it causes idr_replace()
>> return -EINVAL even the id is actually valid.
>
>   idr_replace() open-codes the logic to calculate the maximum valid ID
>   given the height of the idr tree; unfortunately, the open-coded logic
>   doesn't account for the fact that the top layer may have unused slots
>   and over-shifts the limit to zero when the tree is at its maximum
>   height.
>
>> The following test code shows it fails to replace the value for id=((1<<27)+42):
>>
>> static void test5(void)
>> {
>>       int id;
>>       DEFINE_IDR(test_idr);
>> #define TEST5_START ((1<<27)+42) /* use the highest layer */
>>
>>       printk(KERN_INFO "Start test5\n");
>>       id = idr_alloc(&test_idr, (void *)1, TEST5_START, 0, GFP_KERNEL);
>>       BUG_ON(id != TEST5_START);
>>       TEST_BUG_ON(idr_replace(&test_idr, (void *)2, TEST5_START) != (void *)1);
>>       idr_destroy(&test_idr);
>>       printk(KERN_INFO "End of test5\n");
>> }

Does the above testing code need to be kept in the changelog.

Thanks,
Lai

>>
>> Fixed the bug by using idr_max() instead of the incorrect open code.
>
>   Fix the bug by using idr_max() which correctly takes into account the
>   maximum allowed shift.
>
>> There is the same problem in sub_alloc(). The overflow causes sub_alloc()
>> returns -EAGAIN unexpectedly. But the idr_get_empty_slot() will call it
>> again with increased @id. So the bug is hided.
>
>   sub_alloc() shares the same problem and may incorrectly fail with
>   -EAGAIN; however, this bug doesn't affect correct operation because
>   idr_get_empty_slot(), which already uses idr_max(), retries with the
>   increased @id in such cases.
>
>> CC: stable@...r.kernel.org
>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>
>  Acked-by: Tejun Heo <tj@...nel.org>
>
> Thanks.
>
> --
> tejun
> --
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