2018-07-20 09:28:28

by Tomas Bortoli

Subject: [PATCH] [V9fs-developer] [PATCH] /net/9p/trans_fd.c: fix race-condition by flushing workqueue before the kfree()

The patch adds the flush in p9_mux_poll_stop() as it the function used by
p9_conn_destroy(), in turn called by p9_fd_close() to stop the async
polling associated with the data regarding the connection.

Signed-off-by: Tomas Bortoli <[email protected]>
Reported-by: [email protected]
---
As shown by Syzbot, it is possible to provoke a race between p9_fd_close()
and p9_poll_workfn() that is called to take care of the async read/write work
to do. To make sure p9_fd_close() frees "trans" when it is not used anymore,
it has to explicitly flush p9_poll_work before the kfree().

net/9p/trans_fd.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index bf459ee0feab..a64b01c56e30 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -185,6 +185,8 @@ static void p9_mux_poll_stop(struct p9_conn *m)
spin_lock_irqsave(&p9_poll_lock, flags);
list_del_init(&m->poll_pending_link);
spin_unlock_irqrestore(&p9_poll_lock, flags);
+
+ flush_work(&p9_poll_work);
}

/**
--
2.11.0

2018-07-23 02:40:33

by Dominique Martinet

Subject: Re: [PATCH] [V9fs-developer] [PATCH] /net/9p/trans_fd.c: fix race-condition by flushing workqueue before the kfree()

Tomas Bortoli wrote on Fri, Jul 20, 2018:
> The patch adds the flush in p9_mux_poll_stop() as it the function used by
> p9_conn_destroy(), in turn called by p9_fd_close() to stop the async
> polling associated with the data regarding the connection.
>
> Signed-off-by: Tomas Bortoli <[email protected]>
> Reported-by: [email protected]

Looks good to me, I'm taking this patch.

If I had to say something, try to aim for slightly shorter subject lines
if possible :)

> ---
> As shown by Syzbot, it is possible to provoke a race between p9_fd_close()
> and p9_poll_workfn() that is called to take care of the async read/write work
> to do. To make sure p9_fd_close() frees "trans" when it is not used anymore,
> it has to explicitly flush p9_poll_work before the kfree().
>
> net/9p/trans_fd.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
> index bf459ee0feab..a64b01c56e30 100644
> --- a/net/9p/trans_fd.c
> +++ b/net/9p/trans_fd.c
> @@ -185,6 +185,8 @@ static void p9_mux_poll_stop(struct p9_conn *m)
> spin_lock_irqsave(&p9_poll_lock, flags);
> list_del_init(&m->poll_pending_link);
> spin_unlock_irqrestore(&p9_poll_lock, flags);
> +
> + flush_work(&p9_poll_work);
> }
>
> /**
--
Dominique Martinet