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Date:   Mon, 22 Apr 2019 23:00:22 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     YueHaibing <yuehaibing@...wei.com>, netdev <netdev@...r.kernel.org>
Subject: Re: BUG: KASAN: use-after-free Read in tun_net_xmit

On Mon, Apr 22, 2019 at 2:41 AM Jason Wang <jasowang@...hat.com> wrote:
>
>
> On 2019/4/22 上午11:57, YueHaibing wrote:
> > We get a KASAN report as below, but don't have any reproducer.
> >
> > Any comments are appreciated.
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in tun_net_xmit+0x1670/0x1750 drivers/net/tun.c:1104
> > Read of size 8 at addr ffff88836cc26a70 by task swapper/3/0
>
>
> Which kernel version did you use? The calltrace points out the a use
> after free for tun_file structure which should be synchronized through
> RCU + RTNL lock.

The tfile socket has to be marked with SOCK_RCU_FREE in order
to fully respect the RCU grace period.

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e9ca1c088d0b..31c3210288cb 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -3431,6 +3431,7 @@ static int tun_chr_open(struct inode *inode,
struct file * file)
        file->private_data = tfile;
        INIT_LIST_HEAD(&tfile->next);

+       sock_set_flag(&tfile->sk, SOCK_RCU_FREE);
        sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);

        return 0;

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