Messages in this thread | | | Date | Fri, 18 Apr 2014 12:29:30 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH 1/8] idr: fix overflow bug for the max-high layer |
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Hello,
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"); > } > > 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@vger.kernel.org > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Tejun Heo <tj@kernel.org>
Thanks.
-- tejun
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