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SubjectRe: [PATCH net V2] tun: fix use after free for ptr_ring
On Thu, May 10, 2018 at 7:49 PM, Jason Wang <jasowang@redhat.com> wrote:
> static void __tun_detach(struct tun_file *tfile, bool clean)
> {
> struct tun_file *ntfile;
> @@ -736,7 +727,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
> tun->dev->reg_state == NETREG_REGISTERED)
> unregister_netdevice(tun->dev);
> }
> - tun_cleanup_tx_ring(tfile);
> + if (tun)
> + xdp_rxq_info_unreg(&tfile->xdp_rxq);
> sock_put(&tfile->sk);
> }
> }
> @@ -783,14 +775,14 @@ static void tun_detach_all(struct net_device *dev)
> tun_napi_del(tun, tfile);
> /* Drop read queue */
> tun_queue_purge(tfile);
> + xdp_rxq_info_unreg(&tfile->xdp_rxq);
> sock_put(&tfile->sk);
> - tun_cleanup_tx_ring(tfile);
> }
> list_for_each_entry_safe(tfile, tmp, &tun->disabled, next) {
> tun_enable_queue(tfile);
> tun_queue_purge(tfile);
> + xdp_rxq_info_unreg(&tfile->xdp_rxq);
> sock_put(&tfile->sk);
> - tun_cleanup_tx_ring(tfile);

Are you sure this is safe?

xdp_rxq_info_unreg() can't be called more than once either,
please make sure the warning that commit c13da21cdb80
("tun: avoid calling xdp_rxq_info_unreg() twice") fixed will not
show up again.

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