On Mon, 7 Oct 2019 12:21:05 -0700, Eric Dumazet wrote:
> syzbot reported a warning [1] that triggered after recent Jiri patch.
>
> This exposes a bug that we hit already in the past (see commit
> ff244c6b29b1 ("tun: handle register_netdevice() failures properly")
> for details)
>
> tun uses priv->destructor without an ndo_init() method.
>
> register_netdevice() can return an error, but will
> not call priv->destructor() in some cases. Jiri recent
> patch added one more.
>
> A long term fix would be to transfer the initialization
> of what we destroy in ->destructor() in the ndo_init()
>
> This looks a bit risky given the complexity of tun driver.
>
> A simpler fix is to detect after the failed register_netdevice()
> if the tun_free_netdev() function was called already.
>
> [...]
>
> Fixes: ff92741270bf ("net: introduce name_node struct to be used in hashlist")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Cc: Jiri Pirko <j...@mellanox.com>
> Reported-by: syzbot <syzkal...@googlegroups.com>
Looks good, obviously. Presumably we could remove the workaround added
by commit 0ad646c81b21 ("tun: call dev_get_valid_name() before
register_netdevice()") at this point? What are your thoughts on that?
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index
> 812dc3a65efbb9d1ee2724e73978dbc4803ec171..1e541b08b136364302aa524e31efb62062c43faa
> 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2290,7 +2290,13 @@ static void tun_free_netdev(struct net_device *dev)
> struct tun_struct *tun = netdev_priv(dev);
>
> BUG_ON(!(list_empty(&tun->disabled)));
> +
> free_percpu(tun->pcpu_stats);
> + /* We clear pcpu_stats so that tun_set_iff() can tell if
> + * tun_free_netdev() has been called from register_netdevice().
> + */
> + tun->pcpu_stats = NULL;
> +
> tun_flow_uninit(tun);
> security_tun_dev_free_security(tun->security);
> __tun_set_ebpf(tun, &tun->steering_prog, NULL);
> @@ -2859,8 +2865,12 @@ static int tun_set_iff(struct net *net, struct file
> *file, struct ifreq *ifr)
>
> err_detach:
> tun_detach_all(dev);
> - /* register_netdevice() already called tun_free_netdev() */
> - goto err_free_dev;
> + /* We are here because register_netdevice() has failed.
> + * If register_netdevice() already called tun_free_netdev()
> + * while dealing with the error, tun->pcpu_stats has been cleared.
> + */
> + if (!tun->pcpu_stats)
> + goto err_free_dev;
>
> err_free_flow:
> tun_flow_uninit(tun);
