[PATCH net-next 1/3] rtnetlink: add AF_PACKET multicast dumps

[Yuyang Huang <sigefriedhyy@gmail.com>]

RTM_GETMULTICAST dumps IPv4 and IPv6 multicast group memberships, but
the device multicast list (dev->mc) is only available through
/proc/net/dev_mcast, so "ip maddr show" still has to parse procfs for
its link-layer entries.

Handle RTM_GETMULTICAST dumps with ifa_family set to AF_PACKET and
report every entry of dev->mc in the existing ifaddrmsg format:

  - IFA_MULTICAST carries the raw link-layer address
  - IFA_MC_USERS carries the entry reference count
  - IFA_F_PERMANENT marks entries added with SIOCADDMULTI
    (netdev_hw_addr::global_use, "static" in "ip maddr")
  - ifa_scope is RT_SCOPE_LINK

This covers every column of /proc/net/dev_mcast. Strict requests are
validated like the IPv4 dump, except that no attributes are accepted;
a non-zero ifa_index restricts the dump to that device. The dump runs
under RCU and netif_addr_lock_bh() and does not need RTNL.

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
---
 net/core/rtnetlink.c | 132 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 81c5a6104dea..5e83232c1504 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -4566,6 +4566,136 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
 	return skb->len ? : ret;
 }
 
+static int rtnl_fill_mcaddr(struct sk_buff *skb, const struct net_device *dev,
+			    const struct netdev_hw_addr *ha, u32 portid,
+			    u32 seq, unsigned int flags)
+{
+	struct ifaddrmsg *ifm;
+	struct nlmsghdr *nlh;
+
+	nlh = nlmsg_put(skb, portid, seq, RTM_GETMULTICAST, sizeof(*ifm),
+			flags);
+	if (!nlh)
+		return -EMSGSIZE;
+
+	ifm = nlmsg_data(nlh);
+	ifm->ifa_family = AF_PACKET;
+	ifm->ifa_prefixlen = 0;
+	ifm->ifa_flags = ha->global_use ? IFA_F_PERMANENT : 0;
+	ifm->ifa_scope = RT_SCOPE_LINK;
+	ifm->ifa_index = dev->ifindex;
+
+	if (nla_put(skb, IFA_MULTICAST, dev->addr_len, ha->addr) ||
+	    nla_put_u32(skb, IFA_MC_USERS, ha->refcount)) {
+		nlmsg_cancel(skb, nlh);
+		return -EMSGSIZE;
+	}
+
+	nlmsg_end(skb, nlh);
+	return 0;
+}
+
+static int rtnl_dump_mcaddr_dev(struct net_device *dev, struct sk_buff *skb,
+				struct netlink_callback *cb, int *s_addr_idx,
+				unsigned int flags)
+{
+	struct netdev_hw_addr *ha;
+	int addr_idx = 0;
+	int err = 0;
+
+	netif_addr_lock_bh(dev);
+	netdev_for_each_mc_addr(ha, dev) {
+		if (addr_idx < *s_addr_idx) {
+			addr_idx++;
+			continue;
+		}
+		err = rtnl_fill_mcaddr(skb, dev, ha, NETLINK_CB(cb->skb).portid,
+				       cb->nlh->nlmsg_seq, flags);
+		if (err < 0)
+			break;
+		addr_idx++;
+	}
+	netif_addr_unlock_bh(dev);
+
+	*s_addr_idx = err < 0 ? addr_idx : 0;
+
+	return err;
+}
+
+static int rtnl_valid_dump_mcaddr_req(const struct nlmsghdr *nlh,
+				      struct netlink_ext_ack *extack,
+				      int *pifindex)
+{
+	struct ifaddrmsg *ifm;
+
+	ifm = nlmsg_payload(nlh, sizeof(*ifm));
+	if (!ifm) {
+		NL_SET_ERR_MSG(extack,
+			       "Invalid header for multicast dump request");
+		return -EINVAL;
+	}
+
+	if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) {
+		NL_SET_ERR_MSG(extack,
+			       "Invalid values in multicast dump header");
+		return -EINVAL;
+	}
+
+	if (nlmsg_attrlen(nlh, sizeof(*ifm))) {
+		NL_SET_ERR_MSG(extack,
+			       "Invalid data after multicast dump header");
+		return -EINVAL;
+	}
+
+	*pifindex = ifm->ifa_index;
+
+	return 0;
+}
+
+static int rtnl_dump_mcaddr(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	struct net *net = sock_net(skb->sk);
+	unsigned int flags = NLM_F_MULTI;
+	struct {
+		unsigned long ifindex;
+		int addr_idx;
+	} *ctx = (void *)cb->ctx;
+	struct net_device *dev;
+	int ifindex = 0;
+	int err = 0;
+
+	if (cb->strict_check) {
+		err = rtnl_valid_dump_mcaddr_req(cb->nlh, cb->extack,
+						 &ifindex);
+		if (err < 0)
+			return err;
+	}
+
+	rcu_read_lock();
+
+	if (ifindex) {
+		cb->answer_flags |= NLM_F_DUMP_FILTERED;
+		flags |= NLM_F_DUMP_FILTERED;
+		dev = dev_get_by_index_rcu(net, ifindex);
+		if (!dev) {
+			err = -ENODEV;
+			goto out;
+		}
+		err = rtnl_dump_mcaddr_dev(dev, skb, cb, &ctx->addr_idx, flags);
+		goto out;
+	}
+
+	for_each_netdev_dump(net, dev, ctx->ifindex) {
+		err = rtnl_dump_mcaddr_dev(dev, skb, cb, &ctx->addr_idx,
+					   flags);
+		if (err < 0)
+			break;
+	}
+out:
+	rcu_read_unlock();
+	return err;
+}
+
 struct sk_buff *rtmsg_ifinfo_build_skb(int type, struct net_device *dev,
 				       unsigned int change,
 				       u32 event, gfp_t flags, int *new_nsid,
@@ -7251,6 +7381,8 @@ static const struct rtnl_msg_handler rtnetlink_rtnl_msg_handlers[] __initconst =
 	{.msgtype = RTM_SETSTATS, .doit = rtnl_stats_set},
 	{.msgtype = RTM_NEWLINKPROP, .doit = rtnl_newlinkprop},
 	{.msgtype = RTM_DELLINKPROP, .doit = rtnl_dellinkprop},
+	{.protocol = PF_PACKET, .msgtype = RTM_GETMULTICAST,
+	 .dumpit = rtnl_dump_mcaddr, .flags = RTNL_FLAG_DUMP_UNLOCKED},
 	{.protocol = PF_BRIDGE, .msgtype = RTM_GETLINK,
 	 .dumpit = rtnl_bridge_getlink},
 	{.protocol = PF_BRIDGE, .msgtype = RTM_DELLINK,
-- 
2.43.0