[IPv6]: Export userland ND options through netlink (RDNSS support)

As discussed before, this patch provides userland with a way to access
relevant options in Router Advertisements, after they are processed
and validated by the kernel. Extra options are processed in a generic
way; this patch only exports RDNSS options described in RFC5006, but
support to control which options are exported could be easily added.

A new rtnetlink message type is defined, to transport Neighbor
Discovery options, along with optional context information. At the
moment only the address of the router sending an RDNSS option is
included, but additional attributes may be later defined, if needed by
new use cases.

Signed-off-by: Pierre Ynard <linkfanel@yahoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 94 insertions, 9 deletions

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index d4acd283111b..6cc33dc83d1c 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -15,9 +15,10 @@
 /*
  *	Changes:
  *
+ *	Pierre Ynard			:	export userland ND options
+ *						through netlink (RDNSS support)
  *	Lars Fenneberg			:	fixed MTU setting on receipt
  *						of an RA.
- *
  *	Janos Farkas			:	kmalloc failure checks
  *	Alexey Kuznetsov		:	state machine reworked
  *						and moved to net/core.
@@ -78,6 +79,9 @@
 #include <net/addrconf.h>
 #include <net/icmp.h>
 
+#include <net/netlink.h>
+#include <linux/rtnetlink.h>
+
 #include <net/flow.h>
 #include <net/ip6_checksum.h>
 #include <linux/proc_fs.h>
@@ -161,6 +165,8 @@ struct ndisc_options {
 	struct nd_opt_hdr *nd_opts_ri;
 	struct nd_opt_hdr *nd_opts_ri_end;
 #endif
+	struct nd_opt_hdr *nd_useropts;
+	struct nd_opt_hdr *nd_useropts_end;
 };
 
 #define nd_opts_src_lladdr	nd_opt_array[ND_OPT_SOURCE_LL_ADDR]
@@ -225,6 +231,22 @@ static struct nd_opt_hdr *ndisc_next_option(struct nd_opt_hdr *cur,
 	return (cur <= end && cur->nd_opt_type == type ? cur : NULL);
 }
 
+static inline int ndisc_is_useropt(struct nd_opt_hdr *opt)
+{
+	return (opt->nd_opt_type == ND_OPT_RDNSS);
+}
+
+static struct nd_opt_hdr *ndisc_next_useropt(struct nd_opt_hdr *cur,
+					     struct nd_opt_hdr *end)
+{
+	if (!cur || !end || cur >= end)
+		return NULL;
+	do {
+		cur = ((void *)cur) + (cur->nd_opt_len << 3);
+	} while(cur < end && !ndisc_is_useropt(cur));
+	return (cur <= end && ndisc_is_useropt(cur) ? cur : NULL);
+}
+
 static struct ndisc_options *ndisc_parse_options(u8 *opt, int opt_len,
 						 struct ndisc_options *ndopts)
 {
@@ -267,14 +289,21 @@ static struct ndisc_options *ndisc_parse_options(u8 *opt, int opt_len,
 			break;
 #endif
 		default:
-			/*
-			 * Unknown options must be silently ignored,
-			 * to accommodate future extension to the protocol.
-			 */
-			ND_PRINTK2(KERN_NOTICE
-				   "%s(): ignored unsupported option; type=%d, len=%d\n",
-				   __FUNCTION__,
-				   nd_opt->nd_opt_type, nd_opt->nd_opt_len);
+			if (ndisc_is_useropt(nd_opt)) {
+				ndopts->nd_useropts_end = nd_opt;
+				if (!ndopts->nd_useropts)
+					ndopts->nd_useropts = nd_opt;
+			} else {
+				/*
+				 * Unknown options must be silently ignored,
+				 * to accommodate future extension to the
+				 * protocol.
+				 */
+				ND_PRINTK2(KERN_NOTICE
+					   "%s(): ignored unsupported option; type=%d, len=%d\n",
+					   __FUNCTION__,
+					   nd_opt->nd_opt_type, nd_opt->nd_opt_len);
+			}
 		}
 		opt_len -= l;
 		nd_opt = ((void *)nd_opt) + l;
@@ -984,6 +1013,53 @@ out:
 	in6_dev_put(idev);
 }
 
+static void ndisc_ra_useropt(struct sk_buff *ra, struct nd_opt_hdr *opt)
+{
+	struct icmp6hdr *icmp6h = (struct icmp6hdr *)skb_transport_header(ra);
+	struct sk_buff *skb;
+	struct nlmsghdr *nlh;
+	struct nduseroptmsg *ndmsg;
+	int err;
+	int base_size = NLMSG_ALIGN(sizeof(struct nduseroptmsg)
+				    + (opt->nd_opt_len << 3));
+	size_t msg_size = base_size + nla_total_size(sizeof(struct in6_addr));
+
+	skb = nlmsg_new(msg_size, GFP_ATOMIC);
+	if (skb == NULL) {
+		err = -ENOBUFS;
+		goto errout;
+	}
+
+	nlh = nlmsg_put(skb, 0, 0, RTM_NEWNDUSEROPT, base_size, 0);
+	if (nlh == NULL) {
+		goto nla_put_failure;
+	}
+
+	ndmsg = nlmsg_data(nlh);
+	ndmsg->nduseropt_family = AF_INET6;
+	ndmsg->nduseropt_icmp_type = icmp6h->icmp6_type;
+	ndmsg->nduseropt_icmp_code = icmp6h->icmp6_code;
+	ndmsg->nduseropt_opts_len = opt->nd_opt_len << 3;
+
+	memcpy(ndmsg + 1, opt, opt->nd_opt_len << 3);
+
+	NLA_PUT(skb, NDUSEROPT_SRCADDR, sizeof(struct in6_addr),
+		&ipv6_hdr(ra)->saddr);
+	nlmsg_end(skb, nlh);
+
+	err = rtnl_notify(skb, 0, RTNLGRP_ND_USEROPT, NULL, GFP_ATOMIC);
+	if (err < 0)
+		goto errout;
+
+	return;
+
+nla_put_failure:
+	nlmsg_free(skb);
+	err = -EMSGSIZE;
+errout:
+	rtnl_set_sk_err(RTNLGRP_ND_USEROPT, err);
+}
+
 static void ndisc_router_discovery(struct sk_buff *skb)
 {
 	struct ra_msg *ra_msg = (struct ra_msg *)skb_transport_header(skb);
@@ -1216,6 +1292,15 @@ skip_defrtr:
 		}
 	}
 
+	if (ndopts.nd_useropts) {
+		struct nd_opt_hdr *opt;
+		for (opt = ndopts.nd_useropts;
+		     opt;
+		     opt = ndisc_next_useropt(opt, ndopts.nd_useropts_end)) {
+				ndisc_ra_useropt(skb, opt);
+		}
+	}
+
 	if (ndopts.nd_opts_tgt_lladdr || ndopts.nd_opts_rh) {
 		ND_PRINTK2(KERN_WARNING
 			   "ICMPv6 RA: invalid RA options");