On Sat, Apr 19, 2014 at 12:29 AM, Tejun Heo <tj@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx
>> Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
>
> Acked-by: Tejun Heo <tj@xxxxxxxxxx>
>
> Thanks.
>
> --
> tejun
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