Add support for PIO p flag

draft-ietf-6man-pio-pflag is adding a new flag to the Prefix Information
Option to signal that the network can allocate a unique IPv6 prefix per
client via DHCPv6-PD (see draft-ietf-v6ops-dhcp-pd-per-device).

When ra_honor_pio_pflag is enabled, the presence of a P-flag causes
SLAAC autoconfiguration to be disabled for that particular PIO.

An automated test has been added in Android (r.android.com/3195335) to
go along with this change.

Cc: Maciej Żenczykowski <[email protected]>
Cc: Lorenzo Colitti <[email protected]>
Cc: David Lamparter <[email protected]>
Cc: Simon Horman <[email protected]>
Signed-off-by: Patrick Rohr <[email protected]>
Reviewed-by: Maciej Żenczykowski <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Patrick Rohr

Documentation/networking/ip-sysctl.rst

@@ -2362,6 +2362,20 @@ ra_honor_pio_life - BOOLEAN
 
 	Default: 0 (disabled)
 
+ra_honor_pio_pflag - BOOLEAN
+	The Prefix Information Option P-flag indicates the network can
+	allocate a unique IPv6 prefix per client using DHCPv6-PD.
+	This sysctl can be enabled when a userspace DHCPv6-PD client
+	is running to cause the P-flag to take effect: i.e. the
+	P-flag suppresses any effects of the A-flag within the same
+	PIO. For a given PIO, P=1 and A=1 is treated as A=0.
+
+	- If disabled, the P-flag is ignored.
+	- If enabled, the P-flag will disable SLAAC autoconfiguration
+	  for the given Prefix Information Option.
+
+	Default: 0 (disabled)
+
 accept_ra_rt_info_min_plen - INTEGER
 	Minimum prefix length of Route Information in RA.
 

include/linux/ipv6.h

@@ -89,6 +89,7 @@ struct ipv6_devconf {
 	__u8		ioam6_enabled;
 	__u8		ndisc_evict_nocarrier;
 	__u8		ra_honor_pio_life;
+	__u8		ra_honor_pio_pflag;
 
 	struct ctl_table_header *sysctl_header;
 };

include/net/addrconf.h

@@ -37,10 +37,14 @@ struct prefix_info {
 		struct __packed {
 #if defined(__BIG_ENDIAN_BITFIELD)
 			__u8	onlink : 1,
-			 	autoconf : 1,
-				reserved : 6;
+				autoconf : 1,
+				routeraddr : 1,
+				preferpd : 1,
+				reserved : 4;
 #elif defined(__LITTLE_ENDIAN_BITFIELD)
-			__u8	reserved : 6,
+			__u8	reserved : 4,
+				preferpd : 1,
+				routeraddr : 1,
 				autoconf : 1,
 				onlink : 1;
 #else

net/ipv6/addrconf.c

@@ -239,6 +239,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
 	.ioam6_id_wide		= IOAM6_DEFAULT_IF_ID_WIDE,
 	.ndisc_evict_nocarrier	= 1,
 	.ra_honor_pio_life	= 0,
+	.ra_honor_pio_pflag	= 0,
 };
 
 static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
@@ -302,6 +303,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
 	.ioam6_id_wide		= IOAM6_DEFAULT_IF_ID_WIDE,
 	.ndisc_evict_nocarrier	= 1,
 	.ra_honor_pio_life	= 0,
+	.ra_honor_pio_pflag	= 0,
 };
 
 /* Check if link is ready: is it up and is a valid qdisc available */
@@ -2762,6 +2764,7 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao)
 	u32 addr_flags = 0;
 	struct inet6_dev *in6_dev;
 	struct net *net = dev_net(dev);
+	bool ignore_autoconf = false;
 
 	pinfo = (struct prefix_info *) opt;
 
@@ -2864,7 +2867,8 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao)
 
 	/* Try to figure out our local address for this prefix */
 
-	if (pinfo->autoconf && in6_dev->cnf.autoconf) {
+	ignore_autoconf = READ_ONCE(in6_dev->cnf.ra_honor_pio_pflag) && pinfo->preferpd;
+	if (pinfo->autoconf && in6_dev->cnf.autoconf && !ignore_autoconf) {
 		struct in6_addr addr;
 		bool tokenized = false, dev_addr_generated = false;
 
@@ -6926,6 +6930,15 @@ static const struct ctl_table addrconf_sysctl[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_ONE,
 	},
+	{
+		.procname	= "ra_honor_pio_pflag",
+		.data		= &ipv6_devconf.ra_honor_pio_pflag,
+		.maxlen		= sizeof(u8),
+		.mode		= 0644,
+		.proc_handler	= proc_dou8vec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
 #ifdef CONFIG_IPV6_ROUTER_PREF
 	{
 		.procname	= "accept_ra_rtr_pref",