Re: POSSIBLE BUG: selftests/net/fcnal-test.sh: [FAIL] in vrf "bind - ns-B IPv6 LLA" test

[Mirsad Todorovac]

On 6/6/23 16:11, Guillaume Nault wrote:
> On Tue, Jun 06, 2023 at 03:57:35PM +0200, Mirsad Todorovac wrote:
> > diff --git a/net/ipv6/ping.c b/net/ipv6/ping.c
> > index c4835dbdfcff..c1d81c49b775 100644
> > --- a/net/ipv6/ping.c
> > +++ b/net/ipv6/ping.c
> > @@ -73,6 +73,10 @@ static int ping_v6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
> >          struct rt6_info *rt;
> >          struct pingfakehdr pfh;
> >          struct ipcm6_cookie ipc6;
> > +       struct net *net = sock_net(sk);
> > +       struct net_device *dev = NULL;
> > +       struct net_device *mdev = NULL;
> > +       struct net_device *bdev = NULL;
> >
> >          err = ping_common_sendmsg(AF_INET6, msg, len, &user_icmph,
> >                                    sizeof(user_icmph));
> > @@ -111,10 +115,26 @@ static int ping_v6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
> >          else if (!oif)
> >                  oif = np->ucast_oif;
> >
> > +       if (oif) {
> > +               rcu_read_lock();
> > +               dev = dev_get_by_index_rcu(net, oif);
> > +               rcu_read_unlock();
>
> You can't assume '*dev' is still valid after rcu_read_unlock() unless
> you hold a reference on it.
>
> > +               rtnl_lock();
> > +               mdev = netdev_master_upper_dev_get(dev);
> > +               rtnl_unlock();
>
> Because of that, 'dev' might have already disappeared at the time
> netdev_master_upper_dev_get() is called. So it may dereference an
> invalid pointer here.

Good point, thanks. I didn't expect those to change.

This can be fixed, provided that RCU and RTNL locks can be nested:

        rcu_read_lock();
        if (oif) {
                dev = dev_get_by_index_rcu(net, oif);
                rtnl_lock();
                mdev = netdev_master_upper_dev_get(dev);
                rtnl_unlock();
        }

        if (sk->sk_bound_dev_if) {
                bdev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if);
        }

        addr_type = ipv6_addr_type(daddr);
        if ((__ipv6_addr_needs_scope_id(addr_type) && !oif) ||
            (addr_type & IPV6_ADDR_MAPPED) ||
            (oif && sk->sk_bound_dev_if && oif != sk->sk_bound_dev_if &&
                    !(mdev && sk->sk_bound_dev_if && bdev && mdev == bdev))) {
                rcu_read_unlock();
                return -EINVAL;
	}
        rcu_read_unlock();

But again this is still probably not race-free (bdev might also disappear before
the mdev == bdev test), even if it passed fcnal-test.sh, there is much duplication
of code, so your one-line solution is obviously by far better. :-)

Much obliged.

Best regards,
Mirsad

> > +       }
> > +
> > +       if (sk->sk_bound_dev_if) {
> > +               rcu_read_lock();
> > +               bdev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if);
> > +               rcu_read_unlock();
> > +       }
> > +
> >          addr_type = ipv6_addr_type(daddr);
> >          if ((__ipv6_addr_needs_scope_id(addr_type) && !oif) ||
> >              (addr_type & IPV6_ADDR_MAPPED) ||
> > -           (oif && sk->sk_bound_dev_if && oif != sk->sk_bound_dev_if))
> > +           (oif && sk->sk_bound_dev_if && oif != sk->sk_bound_dev_if &&
> > +                   !(mdev && sk->sk_bound_dev_if && bdev && mdev == bdev)))
> >                  return -EINVAL;
> >
> >          ipcm6_init_sk(&ipc6, np);
> >
> > However, this works by the test (888 passed) but your two liner is obviously
> > better :-)
>
> :)

--
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu

System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia