Re: [PATCH] workqueue: Try to catch flush_work() without INIT_WORK().

[Daniel Jordan]

On Wed, Jan 23, 2019 at 09:44:12AM +0900, Tetsuo Handa wrote:
> Daniel Jordan wrote:
> > On Sat, Jan 19, 2019 at 11:41:22AM +0900, Tetsuo Handa wrote:
> > > On 2019/01/19 4:48, Daniel Jordan wrote:
> > > > On Sat, Jan 19, 2019 at 02:04:58AM +0900, Tetsuo Handa wrote:
> > > > __queue_work has a sanity check already for work, but using list_empty.  Seems
> > > > slightly better to be consistent?
> > > > 
> > > 
> > > list_empty() won't work, for "struct work_struct" is embedded into a struct
> > > which is allocated by kzalloc().
> > 
> > Please check list_empty's definition again, it compares the address of the node
> > to its next pointer, so it should work for a zeroed node.  I'll reiterate that
> > it seems slightly better to be consistent in "is work_struct initialized?"
> > checks, but it's not a big deal and I'm fine either way.
> 
> You are talking about
> 
> 	if (WARN_ON(!list_empty(&work->entry))) {
> 		spin_unlock(&pwq->pool->lock);
> 		return;
> 	}
> 
> part in __queue_work(), aren't you? But since flush_work() is used for waiting for
> a work to complete, that work can be either queued state (list_empty() == false) or
> not queued state (list_empty() == true). Thus, I don't think that flush_work() can
> use list_empty() for checking whether that work was initialized.

Oh, you're right, sorry for the noise!

> [PATCH v2] workqueue: Try to catch flush_work() without INIT_WORK().
> 
> syzbot found a flush_work() caller who forgot to call INIT_WORK()
> because that work_struct was allocated by kzalloc() [1]. But the message
> 
>   INFO: trying to register non-static key.
>   the code is fine but needs lockdep annotation.
>   turning off the locking correctness validator.
> 
> by lock_map_acquire() is failing to tell that INIT_WORK() is missing.
> 
> Since flush_work() without INIT_WORK() is a bug, and INIT_WORK() should
> set ->func field to non-zero, let's warn if ->func field is zero.
> 
> [1] https://syzkaller.appspot.com/bug?id=a5954455fcfa51c29ca2ab55b203076337e1c770
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> ---
>  kernel/workqueue.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 392be4b..a503ad9 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2908,6 +2908,9 @@ static bool __flush_work(struct work_struct *work, bool from_cancel)
>  	if (WARN_ON(!wq_online))
>  		return false;
>  
> +	if (WARN_ON(!work->func))
> +		return false;
> +
>  	if (!from_cancel) {
>  		lock_map_acquire(&work->lockdep_map);
>  		lock_map_release(&work->lockdep_map);

Thanks for updating the changelog.  FWIW, you can add

Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>