Re: [PATCH 1/1] kernel/module.c: wakeup processes in module_wq on module unload

[Prarit Bhargava]

On 11/13/19 4:29 AM, Konstantin Khorenko wrote:
> Fix the race between load and unload a kernel module.
> 
> sys_delete_module()
>  try_stop_module()
>   mod->state = _GOING
> 					add_unformed_module()
> 					 old = find_module_all()
> 					 (old->state == _GOING =>
> 					  wait_event_interruptible())
> 
> 					 During pre-condition
> 					 finished_loading() rets 0
> 					 schedule()
> 					 (never gets waken up later)
>  free_module()
>   mod->state = _UNFORMED
>    list_del_rcu(&mod->list)
>    (dels mod from "modules" list)
> 
> return
> 
> The race above leads to modprobe hanging forever on loading
> a module.
> 
> Error paths on loading module call wake_up_all(&module_wq) after
> freeing module, so let's do the same on straight module unload.
> 
> Fixes: 6e6de3dee51a ("kernel/module.c: Only return -EEXIST
> for modules that have finished loading")
> 
> Signed-off-by: Konstantin Khorenko <khorenko@xxxxxxxxxxxxx>
> ---
>  kernel/module.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index ff2d7359a418..cb09a5f37a5f 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1033,6 +1033,8 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
>  	strlcpy(last_unloaded_module, mod->name, sizeof(last_unloaded_module));
>  
>  	free_module(mod);
> +	/* someone could wait for the module in add_unformed_module() */
> +	wake_up_all(&module_wq);

free_module() acts on that *this* module so it makes sense to include the
wake_up_all(&module_wq) call in delete_module.  IIRC I did try a module load &
unload stress test but it looks like my testing wasn't hard enough :(

In any case,

Reviewed-by: Prarit Bhargava <prarit@xxxxxxxxxx>

P.

>  	return 0;
>  out:
>  	mutex_unlock(&module_mutex);
>