linux-kernel - Re: [PATCH] workqueue: Try to catch flush_work() without INIT

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Date:   Wed, 23 Jan 2019 09:44:12 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Try to catch flush_work() without INIT_WORK().

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.

[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@...ove.SAKURA.ne.jp>
---
 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);