netdev - Re: [PATCH net-next v2 06/10] net: IP[V6]_MULTICAST_IF constraint on unbound socket if VRFs present

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Date:   Tue, 2 Oct 2018 13:59:26 -0600
From:   David Ahern <dsahern@...il.com>
To:     Mike Manning <mmanning@...tta.att-mail.com>, netdev@...r.kernel.org
Cc:     Duncan Eastoe <deastoe@...tta.att-mail.com>
Subject: Re: [PATCH net-next v2 06/10] net: IP[V6]_MULTICAST_IF constraint on
 unbound socket if VRFs present

On 10/1/18 2:43 AM, Mike Manning wrote:
> From: Duncan Eastoe <deastoe@...tta.att-mail.com>
> 
> If setsockopt(IP_MULTICAST_IF) or setsockopt(IPV6_MULTICAST_IF) is
> called on a socket which is not bound to a VRF then we should ensure
> that the output device chosen is also not bound to a VRF master.

Why does it matter? An app can set IP_MULTICAST_IF on the socket in the
same way it can set the device bind.

This breaks existing apps.


> 
> This avoids inadvertently sending traffic out of the wrong interface.
> This can be particularly problematic for IP_MULTICAST_IF since the
> interface lookup can be performed by address as well as ifindex. If
> there are interfaces with the same address, one unbound and one bound
> to a VRF, then the interface bound to the VRF may be chosen when the
> sockopt is called on an unbound socket.
> 
> Signed-off-by: Duncan Eastoe <deastoe@...tta.att-mail.com>
> Signed-off-by: Mike Manning <mmanning@...tta.att-mail.com>
> ---
>  net/ipv4/ip_sockglue.c   | 3 +++
>  net/ipv6/ipv6_sockglue.c | 3 +++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> index c0fe5ad996f2..026971314c43 100644
> --- a/net/ipv4/ip_sockglue.c
> +++ b/net/ipv4/ip_sockglue.c
> @@ -892,6 +892,9 @@ static int do_ip_setsockopt(struct sock *sk, int level,
>  		dev_put(dev);
>  
>  		err = -EINVAL;
> +		if (!sk->sk_bound_dev_if && midx)
> +			break;
> +
>  		if (sk->sk_bound_dev_if &&
>  		    mreq.imr_ifindex != sk->sk_bound_dev_if &&
>  		    (!midx || midx != sk->sk_bound_dev_if))
> diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> index c0cac9cc3a28..7dfbc797b130 100644
> --- a/net/ipv6/ipv6_sockglue.c
> +++ b/net/ipv6/ipv6_sockglue.c
> @@ -626,6 +626,9 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
>  
>  			rcu_read_unlock();
>  
> +			if (!sk->sk_bound_dev_if && midx)
> +				goto e_inval;
> +
>  			if (sk->sk_bound_dev_if &&
>  			    sk->sk_bound_dev_if != val &&
>  			    (!midx || midx != sk->sk_bound_dev_if))
>