# Re: \[syzbot\] KASAN: use-after-free Read in nbd\_genl\_connect (2)

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2021-08-25 09:27:37 
- List: linux-block
- Page: https://ratatoskr.run/linux-block/2021/08/1488437
- Thread: https://ratatoskr.run/linux-block/2021/08/1488437/t.md

```text
On Wed, Aug 25, 2021 at 04:55:25PM +0800, Hillf Danton wrote:
> Because no nbd is kfreed without being removed from the nbd idr, finding
> a freed nbd in the idr with nbd_index_mutex held means the nbd is not a
> valid pointer, and fix the uaf by cutting the chance for invalid nbd.
> 
> Only for thoughts now.

That is a bug, but not really the problem here.  I think the issue
is the completion issue that Tetsuo reported.  Looking into that at
the moment.
```