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

From: Guillaume Nault <[email-masked]>
Date: Tue, 6 Jun 2023 16:11:24 +0200

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.

> +       }
> +
> +       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 :-)

:)

> Best regards,
> Mirsad
> 
> -- 
> 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
>