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Subject[PATCH 3.12 121/181] idr: fix overflow bug during maximum ID calculation at maximum height
Date
From: Lai Jiangshan <laijs@cn.fujitsu.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit 3afb69cb5572b3c8c898c00880803cf1a49852c4 upstream.

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");
}

Fix the bug by using idr_max() which correctly takes into account the
maximum allowed shift.

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.

[tj@kernel.org: Updated patch description.]
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
lib/idr.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/lib/idr.c b/lib/idr.c
index bfe4db4e165f..674c30bc2ed0 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -250,7 +250,7 @@ static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa,
id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;

/* if already at the top layer, we need to grow */
- if (id >= 1 << (idp->layers * IDR_BITS)) {
+ if (id > idr_max(idp->layers)) {
*starting_id = id;
return -EAGAIN;
}
@@ -827,12 +827,10 @@ void *idr_replace(struct idr *idp, void *ptr, int id)
if (!p)
return ERR_PTR(-EINVAL);

- n = (p->layer+1) * IDR_BITS;
-
- if (id >= (1 << n))
+ if (id > idr_max(p->layer + 1))
return ERR_PTR(-EINVAL);

- n -= IDR_BITS;
+ n = p->layer * IDR_BITS;
while ((n > 0) && p) {
p = p->ary[(id >> n) & IDR_MASK];
n -= IDR_BITS;
--
2.0.0


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