Re: [PATCH net V2] tun: fix use after free for ptr_ring

[David Miller]

From: Jason Wang <jasowang@xxxxxxxxxx>
Date: Fri, 11 May 2018 10:49:25 +0800

> We used to initialize ptr_ring during TUNSETIFF, this is because its
> size depends on the tx_queue_len of netdevice. And we try to clean it
> up when socket were detached from netdevice. A race were spotted when
> trying to do uninit during a read which will lead a use after free for
> pointer ring. Solving this by always initialize a zero size ptr_ring
> in open() and do resizing during TUNSETIFF, and then we can safely do
> cleanup during close(). With this, there's no need for the workaround
> that was introduced by commit 4df0bfc79904 ("tun: fix a memory leak
> for tfile->tx_array").
> 
> Reported-by: syzbot+e8b902c3c3fadf0a9dba@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Fixes: 1576d9860599 ("tun: switch to use skb array for tx")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>

Jason, please address Cong Wang's concerns.

Thank you.