netdev - Re: [PATCH net V2] vhost: correctly remove wait queue during poll failure

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Message-ID: <20180327130703.g5h2npkp2bnvvebg@dhcp-10-175-199-170.vpn.oracle.com>
Date:   Tue, 27 Mar 2018 14:07:03 +0100
From:   Darren Kenny <darren.kenny@...cle.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net V2] vhost: correctly remove wait queue during poll
 failure

On Tue, Mar 27, 2018 at 08:50:52PM +0800, Jason Wang wrote:
>We tried to remove vq poll from wait queue, but do not check whether
>or not it was in a list before. This will lead double free. Fixing
>this by switching to use vhost_poll_stop() which zeros poll->wqh after
>removing poll from waitqueue to make sure it won't be freed twice.
>
>Cc: Darren Kenny <darren.kenny@...cle.com>
>Reported-by: syzbot+c0272972b01b872e604a@...kaller.appspotmail.com
>Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting backend")
>Signed-off-by: Jason Wang <jasowang@...hat.com>

Reviewed-by: Darren Kenny <darren.kenny@...cle.com>

>---
>Changes from V1:
>- tweak the commit log for to match the code
>---
> drivers/vhost/vhost.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
>diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>index 1b3e8d2d..5d5a9d9 100644
>--- a/drivers/vhost/vhost.c
>+++ b/drivers/vhost/vhost.c
>@@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, struct file *file)
> 	if (mask)
> 		vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
> 	if (mask & EPOLLERR) {
>-		if (poll->wqh)
>-			remove_wait_queue(poll->wqh, &poll->wait);
>+		vhost_poll_stop(poll);
> 		ret = -EINVAL;
> 	}
>
>-- 
>2.7.4
>