If the ida has at least one existed_id, and when an special unallocated_id
is passed to the ida_remove(), the system will crash because it hits NULL
pointer dereference.
This special unallocated_id is that it shares the same lowest idr layer with
an exsited_id, but the idr slot is different(if the unallocated_id is
allocated).
In this case the supposed idr slot of the unallocated_id is NULL,
It means @bitmap == NULL, and when the code dereference it, it crash the kernel.
See the test code:
static void test3(void)
{
int id;
DEFINE_IDA(test_ida);
printk(KERN_INFO "Start test3\n");
if (ida_pre_get(&test_ida, GFP_KERNEL) < 0) return;
if (ida_get_new(&test_ida, &id) < 0) return;
ida_remove(&test_ida, 4000); /* bug: null deference here */
printk(KERN_INFO "End of test3\n");
}
It only happens when unallocated_id, it is caller's fault. It is not
a bug. But it is better to add the proper check and complains instead
of crashing the kernel.
Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
lib/idr.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/lib/idr.c b/lib/idr.c
index a28036d..d200d67 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -1045,7 +1045,7 @@ void ida_remove(struct ida *ida, int id)
__clear_bit(n, p->bitmap);
bitmap = (void *)p->ary[n];
- if (!test_bit(offset, bitmap->bitmap))
+ if (!bitmap || !test_bit(offset, bitmap->bitmap))
goto err;
/* update bitmap and remove it if empty */
--
1.7.4.4
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