Re: [PATCH net-next v2 1/2] netlink: ipv4 igmp join notifications

[Roopa Prabhu <roopa@cumulusnetworks.com>]

On Fri, Aug 31, 2018 at 4:20 AM, Patrick Ruddy
<pruddy@vyatta.att-mail.com> wrote:
> Some userspace applications need to know about IGMP joins from the kernel
> for 2 reasons
> 1. To allow the programming of multicast MAC filters in hardware
> 2. To form a multicast FORUS list for non link-local multicast
>    groups to be sent to the kernel and from there to the interested
>    party.
> (1) can be fulfilled but simply sending the hardware multicast MAC
> address to be programmed but (2) requires the L3 address to be sent
> since this cannot be constructed from the MAC address whereas the
> reverse translation is a standard library function.
>
> This commit provides addition and deletion of multicast addresses
> using the RTM_NEWADDR and RTM_DELADDR messages. It also provides
> the RTM_GETADDR extension to allow multicast join state to be read
> from the kernel.
>
> Signed-off-by: Patrick Ruddy <pruddy@vyatta.att-mail.com>
> ---
> v2: fix kbuild warnings.

I am still going through the series, but AFAICT, user-space caches listening to
RTNLGRP_IPV4_IFADDR will now also get multicast addresses by default ?


>
>  include/linux/igmp.h |  4 ++
>  net/ipv4/devinet.c   | 39 +++++++++++++------
>  net/ipv4/igmp.c      | 90 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 122 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/igmp.h b/include/linux/igmp.h
> index 119f53941c12..644a548024ed 100644
> --- a/include/linux/igmp.h
> +++ b/include/linux/igmp.h
> @@ -19,6 +19,8 @@
>  #include <linux/timer.h>
>  #include <linux/in.h>
>  #include <linux/refcount.h>
> +#include <linux/netlink.h>
> +#include <linux/netdevice.h>
>  #include <uapi/linux/igmp.h>
>
>  static inline struct igmphdr *igmp_hdr(const struct sk_buff *skb)
> @@ -130,6 +132,8 @@ extern void ip_mc_unmap(struct in_device *);
>  extern void ip_mc_remap(struct in_device *);
>  extern void ip_mc_dec_group(struct in_device *in_dev, __be32 addr);
>  extern void ip_mc_inc_group(struct in_device *in_dev, __be32 addr);
> +extern int ip_mc_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb,
> +                            struct net_device *dev);
>  int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed);
>
>  #endif
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index ea4bd8a52422..42f7dcc4fb5e 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -57,6 +57,7 @@
>  #endif
>  #include <linux/kmod.h>
>  #include <linux/netconf.h>
> +#include <linux/igmp.h>
>
>  #include <net/arp.h>
>  #include <net/ip.h>
> @@ -1651,6 +1652,7 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
>         int h, s_h;
>         int idx, s_idx;
>         int ip_idx, s_ip_idx;
> +       int multicast, mcast_idx;
>         struct net_device *dev;
>         struct in_device *in_dev;
>         struct in_ifaddr *ifa;
> @@ -1659,6 +1661,8 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
>         s_h = cb->args[0];
>         s_idx = idx = cb->args[1];
>         s_ip_idx = ip_idx = cb->args[2];
> +       multicast = cb->args[3];
> +       mcast_idx = cb->args[4];
>
>         for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
>                 idx = 0;
> @@ -1675,18 +1679,29 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
>                         if (!in_dev)
>                                 goto cont;
>
> -                       for (ifa = in_dev->ifa_list, ip_idx = 0; ifa;
> -                            ifa = ifa->ifa_next, ip_idx++) {
> -                               if (ip_idx < s_ip_idx)
> -                                       continue;
> -                               if (inet_fill_ifaddr(skb, ifa,
> -                                            NETLINK_CB(cb->skb).portid,
> -                                            cb->nlh->nlmsg_seq,
> -                                            RTM_NEWADDR, NLM_F_MULTI) < 0) {
> -                                       rcu_read_unlock();
> -                                       goto done;
> +                       if (!multicast) {
> +                               for (ifa = in_dev->ifa_list, ip_idx = 0; ifa;
> +                                    ifa = ifa->ifa_next, ip_idx++) {
> +                                       if (ip_idx < s_ip_idx)
> +                                               continue;
> +                                       if (inet_fill_ifaddr(skb, ifa,
> +                                                            NETLINK_CB(cb->skb).portid,
> +                                                            cb->nlh->nlmsg_seq,
> +                                                            RTM_NEWADDR,
> +                                                            NLM_F_MULTI) < 0) {
> +                                               rcu_read_unlock();
> +                                               goto done;
> +                                       }
> +                                       nl_dump_check_consistent(cb,
> +                                                                nlmsg_hdr(skb));
>                                 }
> -                               nl_dump_check_consistent(cb, nlmsg_hdr(skb));
> +                               /* set for multicast loop */
> +                               multicast++;
> +                       }
> +                       /* loop over multicast addresses */
> +                       if (ip_mc_dump_ifaddr(skb, cb, dev) < 0) {
> +                               rcu_read_unlock();
> +                               goto done;
>                         }
>  cont:
>                         idx++;
> @@ -1698,6 +1713,8 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
>         cb->args[0] = h;
>         cb->args[1] = idx;
>         cb->args[2] = ip_idx;
> +       cb->args[3] = multicast;
> +       cb->args[4] = mcast_idx;
>
>         return skb->len;
>  }
> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> index cf75f8944b05..c9bbd1d27124 100644
> --- a/net/ipv4/igmp.c
> +++ b/net/ipv4/igmp.c
> @@ -86,6 +86,7 @@
>  #include <linux/inetdevice.h>
>  #include <linux/igmp.h>
>  #include <linux/if_arp.h>
> +#include <net/netlink.h>
>  #include <linux/rtnetlink.h>
>  #include <linux/times.h>
>  #include <linux/pkt_sched.h>
> @@ -1384,6 +1385,91 @@ static void ip_mc_hash_remove(struct in_device *in_dev,
>  }
>
>
> +static int fill_addr(struct sk_buff *skb, struct net_device *dev, __be32 addr,
> +                    int type, unsigned int flags)
> +{
> +       struct nlmsghdr *nlh;
> +       struct ifaddrmsg *ifm;
> +
> +       nlh = nlmsg_put(skb, 0, 0, type, sizeof(*ifm), flags);
> +       if (!nlh)
> +               return -EMSGSIZE;
> +
> +       ifm = nlmsg_data(nlh);
> +       ifm->ifa_family = AF_INET;
> +       ifm->ifa_prefixlen = 32;
> +       ifm->ifa_flags = IFA_F_PERMANENT;
> +       ifm->ifa_scope = RT_SCOPE_LINK;
> +       ifm->ifa_index = dev->ifindex;
> +
> +       if (nla_put_in_addr(skb, IFA_ADDRESS, addr))
> +               goto nla_put_failure;
> +       nlmsg_end(skb, nlh);
> +       return 0;
> +
> +nla_put_failure:
> +       nlmsg_cancel(skb, nlh);
> +       return -EMSGSIZE;
> +}
> +
> +static inline size_t addr_nlmsg_size(void)
> +{
> +       return NLMSG_ALIGN(sizeof(struct ifaddrmsg))
> +               + nla_total_size(sizeof(__be32));
> +}
> +
> +static void ip_mc_addr_notify(struct net_device *dev, __be32 addr, int type)
> +{
> +       struct net *net = dev_net(dev);
> +       struct sk_buff *skb;
> +       int err = -ENOBUFS;
> +
> +       skb = nlmsg_new(addr_nlmsg_size(), GFP_ATOMIC);
> +       if (!skb)
> +               goto errout;
> +
> +       err = fill_addr(skb, dev, addr, type, 0);
> +       if (err < 0) {
> +               WARN_ON(err == -EMSGSIZE);
> +               kfree_skb(skb);
> +               goto errout;
> +       }
> +       rtnl_notify(skb, net, 0, RTNLGRP_IPV4_IFADDR, NULL, GFP_ATOMIC);
> +       return;
> +errout:
> +       if (err < 0)
> +               rtnl_set_sk_err(net, RTNLGRP_LINK, err);


s/RTNLGRP_LINK/RTNLGRP_IPV4_IFADDR/




> +}
> +
> +int ip_mc_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb,
> +                     struct net_device *dev)
> +{
> +       int s_idx;
> +       int idx = 0;
> +       struct ip_mc_list *im;
> +       struct in_device *in_dev;
> +
> +       ASSERT_RTNL();
> +
> +       s_idx = cb->args[4];
> +       in_dev = __in_dev_get_rtnl(dev);
> +
> +       for_each_pmc_rtnl(in_dev, im) {
> +               if (idx < s_idx)
> +                       continue;
> +               if (fill_addr(skb, dev, im->multiaddr, RTM_NEWADDR,
> +                             NLM_F_MULTI) < 0)
> +                       goto done;
> +               nl_dump_check_consistent(cb, nlmsg_hdr(skb));
> +               idx++;
> +       }
> +
> + done:
> +       cb->args[4] = idx;
> +
> +       return skb->len;
> +}
> +
>  /*
>   *     A socket has joined a multicast group on device dev.
>   */
> @@ -1433,6 +1519,8 @@ static void __ip_mc_inc_group(struct in_device *in_dev, __be32 addr,
>         igmpv3_del_delrec(in_dev, im);
>  #endif
>         igmp_group_added(im);
> +
> +       ip_mc_addr_notify(in_dev->dev, addr, RTM_NEWADDR);
>         if (!in_dev->dead)
>                 ip_rt_multicast_event(in_dev);
>  out:
> @@ -1664,6 +1752,8 @@ void ip_mc_dec_group(struct in_device *in_dev, __be32 addr)
>                                 in_dev->mc_count--;
>                                 igmp_group_dropped(i);
>                                 ip_mc_clear_src(i);
> +                               ip_mc_addr_notify(in_dev->dev, addr,
> +                                                 RTM_DELADDR);
>
>                                 if (!in_dev->dead)
>                                         ip_rt_multicast_event(in_dev);
> --
> 2.17.1
>