net/ipv6: Expand and rename accept_unsolicited_na to accept_untracked_na

RFC 9131 changes default behaviour of handling RX of NA messages when the
corresponding entry is absent in the neighbour cache. The current
implementation is limited to accept just unsolicited NAs. However, the
RFC is more generic where it also accepts solicited NAs. Both types
should result in adding a STALE entry for this case.

Expand accept_untracked_na behaviour to also accept solicited NAs to
be compliant with the RFC and rename the sysctl knob to
accept_untracked_na.

Fixes: f9a2fb73318e ("net/ipv6: Introduce accept_unsolicited_na knob to implement router-side changes for RFC9131")
Signed-off-by: Arun Ajith S <aajith@arista.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20220530101414.65439-1-aajith@arista.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

2 files changed, 28 insertions, 20 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index ca0aa744593e..1b1932502e9e 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5586,7 +5586,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 	array[DEVCONF_IOAM6_ID] = cnf->ioam6_id;
 	array[DEVCONF_IOAM6_ID_WIDE] = cnf->ioam6_id_wide;
 	array[DEVCONF_NDISC_EVICT_NOCARRIER] = cnf->ndisc_evict_nocarrier;
-	array[DEVCONF_ACCEPT_UNSOLICITED_NA] = cnf->accept_unsolicited_na;
+	array[DEVCONF_ACCEPT_UNTRACKED_NA] = cnf->accept_untracked_na;
 }
 
 static inline size_t inet6_ifla6_size(void)
@@ -7038,8 +7038,8 @@ static const struct ctl_table addrconf_sysctl[] = {
 		.extra2		= (void *)SYSCTL_ONE,
 	},
 	{
-		.procname	= "accept_unsolicited_na",
-		.data		= &ipv6_devconf.accept_unsolicited_na,
+		.procname	= "accept_untracked_na",
+		.data		= &ipv6_devconf.accept_untracked_na,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 254addad0dd3..b0dfe97ea4ee 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -979,7 +979,7 @@ static void ndisc_recv_na(struct sk_buff *skb)
 	struct inet6_dev *idev = __in6_dev_get(dev);
 	struct inet6_ifaddr *ifp;
 	struct neighbour *neigh;
-	bool create_neigh;
+	u8 new_state;
 
 	if (skb->len < sizeof(struct nd_msg)) {
 		ND_PRINTK(2, warn, "NA: packet too short\n");
@@ -1000,7 +1000,7 @@ static void ndisc_recv_na(struct sk_buff *skb)
 	/* For some 802.11 wireless deployments (and possibly other networks),
 	 * there will be a NA proxy and unsolicitd packets are attacks
 	 * and thus should not be accepted.
-	 * drop_unsolicited_na takes precedence over accept_unsolicited_na
+	 * drop_unsolicited_na takes precedence over accept_untracked_na
 	 */
 	if (!msg->icmph.icmp6_solicited && idev &&
 	    idev->cnf.drop_unsolicited_na)
@@ -1041,25 +1041,33 @@ static void ndisc_recv_na(struct sk_buff *skb)
 		in6_ifa_put(ifp);
 		return;
 	}
+
+	neigh = neigh_lookup(&nd_tbl, &msg->target, dev);
+
 	/* RFC 9131 updates original Neighbour Discovery RFC 4861.
-	 * An unsolicited NA can now create a neighbour cache entry
-	 * on routers if it has Target LL Address option.
+	 * NAs with Target LL Address option without a corresponding
+	 * entry in the neighbour cache can now create a STALE neighbour
+	 * cache entry on routers.
+	 *
+	 *   entry accept  fwding  solicited        behaviour
+	 * ------- ------  ------  ---------    ----------------------
+	 * present      X       X         0     Set state to STALE
+	 * present      X       X         1     Set state to REACHABLE
+	 *  absent      0       X         X     Do nothing
+	 *  absent      1       0         X     Do nothing
+	 *  absent      1       1         X     Add a new STALE entry
 	 *
-	 * drop   accept  fwding                   behaviour
-	 * ----   ------  ------  ----------------------------------------------
-	 *    1        X       X  Drop NA packet and don't pass up the stack
-	 *    0        0       X  Pass NA packet up the stack, don't update NC
-	 *    0        1       0  Pass NA packet up the stack, don't update NC
-	 *    0        1       1  Pass NA packet up the stack, and add a STALE
-	 *                          NC entry
 	 * Note that we don't do a (daddr == all-routers-mcast) check.
 	 */
-	create_neigh = !msg->icmph.icmp6_solicited && lladdr &&
-		       idev && idev->cnf.forwarding &&
-		       idev->cnf.accept_unsolicited_na;
-	neigh = __neigh_lookup(&nd_tbl, &msg->target, dev, create_neigh);
+	new_state = msg->icmph.icmp6_solicited ? NUD_REACHABLE : NUD_STALE;
+	if (!neigh && lladdr &&
+	    idev && idev->cnf.forwarding &&
+	    idev->cnf.accept_untracked_na) {
+		neigh = neigh_create(&nd_tbl, &msg->target, dev);
+		new_state = NUD_STALE;
+	}
 
-	if (neigh) {
+	if (neigh && !IS_ERR(neigh)) {
 		u8 old_flags = neigh->flags;
 		struct net *net = dev_net(dev);
 
@@ -1079,7 +1087,7 @@ static void ndisc_recv_na(struct sk_buff *skb)
 		}
 
 		ndisc_update(dev, neigh, lladdr,
-			     msg->icmph.icmp6_solicited ? NUD_REACHABLE : NUD_STALE,
+			     new_state,
 			     NEIGH_UPDATE_F_WEAK_OVERRIDE|
 			     (msg->icmph.icmp6_override ? NEIGH_UPDATE_F_OVERRIDE : 0)|
 			     NEIGH_UPDATE_F_OVERRIDE_ISROUTER|