From: Jason Wang <jasowang@redhat•com>
To: Yang Yingliang <yangyingliang@huawei•com>
Cc: David Miller <davem@davemloft•net>,
netdev@vger•kernel.org, eric dumazet <eric.dumazet@gmail•com>,
xiyou wangcong <xiyou.wangcong@gmail•com>,
weiyongjun1@huawei•com
Subject: Re: [PATCH v3] tun: fix use-after-free when register netdev failed
Date: Thu, 22 Aug 2019 23:05:05 -0400 (EDT) [thread overview]
Message-ID: <1676209666.10068041.1566529505528.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <5D5E90C3.50306@huawei.com>
----- Original Message -----
>
>
> On 2019/8/22 14:07, Yang Yingliang wrote:
> >
> >
> > On 2019/8/22 10:13, Jason Wang wrote:
> >>
> >> On 2019/8/20 上午10:28, Jason Wang wrote:
> >>>
> >>> On 2019/8/20 上午9:25, David Miller wrote:
> >>>> From: Yang Yingliang <yangyingliang@huawei•com>
> >>>> Date: Mon, 19 Aug 2019 21:31:19 +0800
> >>>>
> >>>>> Call tun_attach() after register_netdevice() to make sure tfile->tun
> >>>>> is not published until the netdevice is registered. So the read/write
> >>>>> thread can not use the tun pointer that may freed by free_netdev().
> >>>>> (The tun and dev pointer are allocated by alloc_netdev_mqs(), they
> >>>>> can
> >>>>> be freed by netdev_freemem().)
> >>>> register_netdevice() must always be the last operation in the order of
> >>>> network device setup.
> >>>>
> >>>> At the point register_netdevice() is called, the device is visible
> >>>> globally
> >>>> and therefore all of it's software state must be fully initialized and
> >>>> ready for us.
> >>>>
> >>>> You're going to have to find another solution to these problems.
> >>>
> >>>
> >>> The device is loosely coupled with sockets/queues. Each side is
> >>> allowed to be go away without caring the other side. So in this
> >>> case, there's a small window that network stack think the device has
> >>> one queue but actually not, the code can then safely drop them.
> >>> Maybe it's ok here with some comments?
> >>>
> >>> Or if not, we can try to hold the device before tun_attach and drop
> >>> it after register_netdevice().
> >>
> >>
> >> Hi Yang:
> >>
> >> I think maybe we can try to hold refcnt instead of playing real num
> >> queues here. Do you want to post a V4?
> > I think the refcnt can prevent freeing the memory in this case.
> > When register_netdevice() failed, free_netdev() will be called directly,
> > dev->pcpu_refcnt and dev are freed without checking refcnt of dev.
> How about using patch-v1 that using a flag to check whether the device
> registered successfully.
>
As I said, it lacks sufficient locks or barriers. To be clear, I meant
something like (compile-test only):
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index db16d7a13e00..e52678f9f049 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2828,6 +2828,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
(ifr->ifr_flags & TUN_FEATURES);
INIT_LIST_HEAD(&tun->disabled);
+ dev_hold(dev);
err = tun_attach(tun, file, false, ifr->ifr_flags & IFF_NAPI,
ifr->ifr_flags & IFF_NAPI_FRAGS);
if (err < 0)
@@ -2836,6 +2837,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
err = register_netdevice(tun->dev);
if (err < 0)
goto err_detach;
+ dev_put(dev);
}
netif_carrier_on(tun->dev);
@@ -2852,11 +2854,13 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
return 0;
err_detach:
+ dev_put(dev);
tun_detach_all(dev);
/* register_netdevice() already called tun_free_netdev() */
goto err_free_dev;
err_free_flow:
+ dev_put(dev);
tun_flow_uninit(tun);
security_tun_dev_free_security(tun->security);
err_free_stat:
What's your thought?
Thanks
next prev parent reply other threads:[~2019-08-23 3:05 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 13:31 [PATCH v3] tun: fix use-after-free when register netdev failed Yang Yingliang
2019-08-20 1:25 ` David Miller
2019-08-20 2:28 ` Jason Wang
2019-08-22 2:13 ` Jason Wang
2019-08-22 6:07 ` Yang Yingliang
2019-08-22 12:55 ` Yang Yingliang
2019-08-23 3:05 ` Jason Wang [this message]
2019-08-23 9:36 ` Yang Yingliang
2019-09-02 5:32 ` Jason Wang
2019-09-03 1:45 ` Yang Yingliang
2019-09-03 3:03 ` Jason Wang
2019-09-03 5:42 ` Yang Yingliang
2019-09-03 6:06 ` Jason Wang
2019-09-03 7:35 ` Yang Yingliang
2019-09-03 10:50 ` Jason Wang
2019-09-05 2:03 ` Yang Yingliang
2019-09-05 3:10 ` Jason Wang
2019-09-10 2:31 ` Yang Yingliang
2019-09-10 2:36 ` Jason Wang
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