Messages in this thread Patch in this message | | | From | Lai Jiangshan <> | Subject | [PATCH 3/8] idr: fix NULL pointer dereference when ida_remove(unallocated_id) | Date | Fri, 18 Apr 2014 20:49:50 +0800 |
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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 <laijs@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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