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 15:46:52 +0200

On Tue, Jun 06, 2023 at 08:24:54AM +0200, Mirsad Goran Todorovac wrote:
> On 5/31/23 20:11, Guillaume Nault wrote:
> > I believe this condition should be relaxed to allow the case where
> > ->sk_bound_dev_if is oif's master device (and maybe there are other
> > VRF cases to also consider).
> 
> I've tried something like this, but something makes the kernel stuck
> here:
> 
> TEST: ping out, blocked by route - ns-B loopback IPv6                         [ OK ]
> TEST: ping out, device bind, blocked by route - ns-B loopback IPv6            [ OK ]
> TEST: ping in, blocked by route - ns-A loopback IPv6                          [ OK ]
> TEST: ping out, unreachable route - ns-B loopback IPv6                        [ OK ]
> TEST: ping out, device bind, unreachable route - ns-B loopback IPv6           [ OK ]
> 
> #################################################################
> With VRF
> 
> [hanged process and kernel won't shutdown]
> 
> The code is:
> 
> ---
>  net/ipv6/ping.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/ping.c b/net/ipv6/ping.c
> index c4835dbdfcff..81293e902293 100644
> --- a/net/ipv6/ping.c
> +++ b/net/ipv6/ping.c
> @@ -73,6 +73,9 @@ 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;
>         err = ping_common_sendmsg(AF_INET6, msg, len, &user_icmph,
>                                   sizeof(user_icmph));
> @@ -111,10 +114,17 @@ static int ping_v6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
>         else if (!oif)
>                 oif = np->ucast_oif;
> +       if (oif) {
> +               dev = dev_get_by_index(net, oif);
> +               mdev = netdev_master_upper_dev_get(dev);
> +       }
> +
>         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 &&
> +                             mdev != dev_get_by_index(net, sk->sk_bound_dev_if))))
>                 return -EINVAL;
>         ipcm6_init_sk(&ipc6, np);
> 
> I am obviously doing something very stupid.

The problem is that dev_get_by_index() holds a reference on 'dev' which
your code never releases. Also netdev_master_upper_dev_get() needs rtnl
protection. These should have generated some kernel oops.

You can try this instead:

-------- >8 --------

diff --git a/net/ipv6/ping.c b/net/ipv6/ping.c
index c4835dbdfcff..f804c11e2146 100644
--- a/net/ipv6/ping.c
+++ b/net/ipv6/ping.c
@@ -114,7 +114,8 @@ static int ping_v6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	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 &&
+	     l3mdev_master_ifindex_by_index(sock_net(sk), oif) != sk->sk_bound_dev_if))
 		return -EINVAL;
 
 	ipcm6_init_sk(&ipc6, np);