[PATCH net-next v2] ipv6: don't generate link-local addr in random or privacy mode

[Rocco Yue]

In the 3GPP TS 29.061, here is a description as follows:
"In order to avoid any conflict between the link-local address
of the MS and that of the GGSN, the Interface-Identifier used by
the MS to build its link-local address shall be assigned by the
GGSN. The GGSN ensures the uniqueness of this Interface-Identifier.
The MT shall then enforce the use of this Interface-Identifier by
the TE"

In other words, in the cellular network, GGSN determines whether
to reply a solicited RA message by identifying the bottom 64 bits
of the source address of the received RS message. Therefore,
cellular network device's ipv6 link-local address should be set
as the format of fe80::(GGSN assigned IID).

To meet the above spec requirement, this patch adds two new
addr_gen_mode:

1) IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA, this mode is suitable
for cellular networks that support RFC7217. In this mode, the
kernel doesn't generate a link-local address for the cellular
NIC, and generates an ipv6 stable privacy global address after
receiving the RA message.

2) IN6_ADDR_GEN_MODE_RANDOM_NO_LLA, in this mode, the kernel
doesn't generate a link-local address for the cellular NIC,
and will use the bottom 64 bits of the link-local address(same
as the IID assigned by GGSN) to form an ipv6 global address
after receiveing the RA message.

Signed-off-by: Rocco Yue <rocco.yue@xxxxxxxxxxxx>
---
v1->v2: Add new addr_gen_mode instead of adding a separate sysctl.

v1 link:
https://patchwork.kernel.org/patch/12353465

---
 include/uapi/linux/if_link.h       |  2 ++
 net/ipv6/addrconf.c                | 22 ++++++++++++++++------
 tools/include/uapi/linux/if_link.h |  2 ++
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index eebd3894fe89..9c5695744c7d 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -428,6 +428,8 @@ enum in6_addr_gen_mode {
 	IN6_ADDR_GEN_MODE_NONE,
 	IN6_ADDR_GEN_MODE_STABLE_PRIVACY,
 	IN6_ADDR_GEN_MODE_RANDOM,
+	IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
+	IN6_ADDR_GEN_MODE_RANDOM_NO_LLA,
 };
 
 /* Bridge section */
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 3445f8017430..0045de10f4b5 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -392,7 +392,8 @@ static struct inet6_dev *ipv6_add_dev(struct net_device *dev)
 	timer_setup(&ndev->rs_timer, addrconf_rs_timer, 0);
 	memcpy(&ndev->cnf, dev_net(dev)->ipv6.devconf_dflt, sizeof(ndev->cnf));
 
-	if (ndev->cnf.stable_secret.initialized)
+	if (ndev->cnf.stable_secret.initialized &&
+	    ndev->cnf.addr_gen_mode != IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA)
 		ndev->cnf.addr_gen_mode = IN6_ADDR_GEN_MODE_STABLE_PRIVACY;
 
 	ndev->cnf.mtu6 = dev->mtu;
@@ -2578,7 +2579,8 @@ static void manage_tempaddrs(struct inet6_dev *idev,
 static bool is_addr_mode_generate_stable(struct inet6_dev *idev)
 {
 	return idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_STABLE_PRIVACY ||
-	       idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_RANDOM;
+	       idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_RANDOM ||
+	       idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA;
 }
 
 int addrconf_prefix_rcv_add_addr(struct net *net, struct net_device *dev,
@@ -3331,6 +3333,8 @@ static void addrconf_addr_gen(struct inet6_dev *idev, bool prefix_route)
 					      0, 0, GFP_KERNEL);
 		break;
 	case IN6_ADDR_GEN_MODE_NONE:
+	case IN6_ADDR_GEN_MODE_RANDOM_NO_LLA:
+	case IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA:
 	default:
 		/* will not add any link local address */
 		break;
@@ -5798,7 +5802,9 @@ static int check_addr_gen_mode(int mode)
 	if (mode != IN6_ADDR_GEN_MODE_EUI64 &&
 	    mode != IN6_ADDR_GEN_MODE_NONE &&
 	    mode != IN6_ADDR_GEN_MODE_STABLE_PRIVACY &&
-	    mode != IN6_ADDR_GEN_MODE_RANDOM)
+	    mode != IN6_ADDR_GEN_MODE_RANDOM &&
+	    mode != IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA &&
+	    mode != IN6_ADDR_GEN_MODE_RANDOM_NO_LLA)
 		return -EINVAL;
 	return 1;
 }
@@ -6428,15 +6434,19 @@ static int addrconf_sysctl_stable_secret(struct ctl_table *ctl, int write,
 		for_each_netdev(net, dev) {
 			struct inet6_dev *idev = __in6_dev_get(dev);
 
-			if (idev) {
+			if (idev && idev->cnf.addr_gen_mode !=
+			    IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA) {
 				idev->cnf.addr_gen_mode =
 					IN6_ADDR_GEN_MODE_STABLE_PRIVACY;
 			}
 		}
 	} else {
 		struct inet6_dev *idev = ctl->extra1;
-
-		idev->cnf.addr_gen_mode = IN6_ADDR_GEN_MODE_STABLE_PRIVACY;
+		if (idev->cnf.addr_gen_mode !=
+		    IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA) {
+			idev->cnf.addr_gen_mode =
+				IN6_ADDR_GEN_MODE_STABLE_PRIVACY;
+		}
 	}
 
 out:
diff --git a/tools/include/uapi/linux/if_link.h b/tools/include/uapi/linux/if_link.h
index b3610fdd1fee..fb69137aea89 100644
--- a/tools/include/uapi/linux/if_link.h
+++ b/tools/include/uapi/linux/if_link.h
@@ -241,6 +241,8 @@ enum in6_addr_gen_mode {
 	IN6_ADDR_GEN_MODE_NONE,
 	IN6_ADDR_GEN_MODE_STABLE_PRIVACY,
 	IN6_ADDR_GEN_MODE_RANDOM,
+	IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
+	IN6_ADDR_GEN_MODE_RANDOM_NO_LLA,
 };
 
 /* Bridge section */
-- 
2.18.0