[PATCH net-next v2] net/ipv6: Introduce accept_unsolicited_na knob to implement router-side changes for RFC9131
From: Arun Ajith S
Date: Thu Apr 07 2022 - 03:45:16 EST
Add a new neighbour cache entry in STALE state for routers on receiving
an unsolicited (gratuitous) neighbour advertisement with
target link-layer-address option specified.
This is similar to the arp_accept configuration for IPv4.
A new sysctl endpoint is created to turn on this behaviour:
/proc/sys/net/ipv6/conf/interface/accept_unsolicited_na.
Signed-off-by: Arun Ajith S <aajith@xxxxxxxxxx>
Tested-by: Arun Ajith S <aajith@xxxxxxxxxx>
---
Documentation/networking/ip-sysctl.rst | 23 +++++++++++++++++++++++
include/linux/ipv6.h | 1 +
include/uapi/linux/ipv6.h | 1 +
net/ipv6/addrconf.c | 8 ++++++++
net/ipv6/ndisc.c | 20 +++++++++++++++++++-
5 files changed, 52 insertions(+), 1 deletion(-)
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index b0024aa7b051..9e17efe343ac 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2467,6 +2467,29 @@ drop_unsolicited_na - BOOLEAN
By default this is turned off.
+accept_unsolicited_na - BOOLEAN
+ Add a new neighbour cache entry in STALE state for routers on receiving an
+ unsolicited neighbour advertisement with target link-layer address option
+ specified. This is as per router-side behavior documented in RFC9131.
+ This has lower precedence than drop_unsolicited_na.
+ 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
+ This will optimize the return path for the initial off-link communication
+ that is initiated by a directly connected host, by ensuring that
+ the first-hop router which turns on this setting doesn't have to
+ buffer the initial return packets to do neighbour-solicitation.
+ The prerequisite is that the host is configured to send
+ unsolicited neighbour advertisements on interface bringup.
+ This setting should be used in conjunction with the ndisc_notify setting
+ on the host to satisfy this prerequisite.
+
+ By default this is turned off.
+
enhanced_dad - BOOLEAN
Include a nonce option in the IPv6 neighbor solicitation messages used for
duplicate address detection per RFC7527. A received DAD NS will only signal
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 16870f86c74d..918bfea4ef5f 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -61,6 +61,7 @@ struct ipv6_devconf {
__s32 suppress_frag_ndisc;
__s32 accept_ra_mtu;
__s32 drop_unsolicited_na;
+ __s32 accept_unsolicited_na;
struct ipv6_stable_secret {
bool initialized;
struct in6_addr secret;
diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index d4178dace0bf..549ddeaf788b 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -194,6 +194,7 @@ enum {
DEVCONF_IOAM6_ID,
DEVCONF_IOAM6_ID_WIDE,
DEVCONF_NDISC_EVICT_NOCARRIER,
+ DEVCONF_ACCEPT_UNSOLICITED_NA,
DEVCONF_MAX
};
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 1afc4c024981..1b4d278d0454 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5587,6 +5587,7 @@ 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;
}
static inline size_t inet6_ifla6_size(void)
@@ -7037,6 +7038,13 @@ static const struct ctl_table addrconf_sysctl[] = {
.extra1 = (void *)SYSCTL_ZERO,
.extra2 = (void *)SYSCTL_ONE,
},
+ {
+ .procname = "accept_unsolicited_na",
+ .data = &ipv6_devconf.accept_unsolicited_na,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
{
/* sentinel */
}
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index fcb288b0ae13..254addad0dd3 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -979,6 +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;
if (skb->len < sizeof(struct nd_msg)) {
ND_PRINTK(2, warn, "NA: packet too short\n");
@@ -999,6 +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
*/
if (!msg->icmph.icmp6_solicited && idev &&
idev->cnf.drop_unsolicited_na)
@@ -1039,7 +1041,23 @@ 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.
+ *
+ * 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);
if (neigh) {
u8 old_flags = neigh->flags;
--
2.27.0
---
Changes from v1:
- Change bad documentation and commit description. (source link-layer-address option -> target link-layer-address option)
- CCed all maintainers from .scripts/get_maintainer.pl
- Rebased to latest origin/master