Re: [PATCH] netlink: Add netns check on taps

[David Ahern <dsahern@gmail.com>]

On 12/5/17 3:46 PM, Kevin Cernekee wrote:
> Currently, a nlmon link inside a child namespace can observe systemwide
> netlink activity.  Filter the traffic so that in a non-init netns,
> nlmon can only sniff netlink messages from its own netns.
> 
> Test case:
> 
>     vpnns -- bash -c "ip link add nlmon0 type nlmon; \
>                       ip link set nlmon0 up; \
>                       tcpdump -i nlmon0 -q -w /tmp/nlmon.pcap -U" &
>     sudo ip xfrm state add src 10.1.1.1 dst 10.1.1.2 proto esp \
>         spi 0x1 mode transport \
>         auth sha1 0x6162633132330000000000000000000000000000 \
>         enc aes 0x00000000000000000000000000000000
>     grep abc123 /tmp/nlmon.pcap
> 
> Signed-off-by: Kevin Cernekee <cernekee@chromium.org>
> ---
>  net/netlink/af_netlink.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index b9e0ee4..88381a2 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -253,6 +253,11 @@ static int __netlink_deliver_tap_skb(struct sk_buff *skb,
>  	struct sock *sk = skb->sk;
>  	int ret = -ENOMEM;
>  
> +	if (!net_eq(dev_net(dev), sock_net(sk)) &&
> +	    !net_eq(dev_net(dev), &init_net)) {

Why is init_net special? Seems like snooping should be limited to the
namespace you are in.