Re: KASAN: use-after-free Write in config_item_get

[Greg KH]

On Mon, May 11, 2020 at 05:52:16AM +0000, Kyungtae Kim wrote:
> We report a bug (in linux-5.6.8) found by FuzzUSB (a modified version
> of syzkaller)
> 
> kernel config: https://kt0755.github.io/etc/config_v5.6.8
> 
> 
> This bug happened when accessing a configfs_item instance right after being
> deallocated.
> Specifically, config_item_get() tries to access ci_kref element in a config_item instance. 
> But this led to memory access violation because that instance (held by a fsg_opts structure) 
> had been freed by fsg_free_inst() in another thread (PID: 2603).
> 
> To fix, it needs to check if the config_item instance is still in use 
> when trying to deallocate it.

Great, can you create a patch to fix this now that you have a solid test
for it?

thanks,

greg k-h