ipv6 addrconf: implement RFC7559 router solicitation backoff

This implements:
  https://tools.ietf.org/html/rfc7559

Backoff is performed according to RFC3315 section 14:
  https://tools.ietf.org/html/rfc3315#section-14

We allow setting /proc/sys/net/ipv6/conf/*/router_solicitations
to a negative value meaning an unlimited number of retransmits,
and we make this the new default (inline with the RFC).

We also add a new setting:
  /proc/sys/net/ipv6/conf/*/router_solicitation_max_interval
defaulting to 1 hour (per RFC recommendation).

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Acked-by: Erik Kline <ek@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 49 insertions, 8 deletions

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index c6dbcd84a2c7..7e9a789be5e0 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -18,6 +18,7 @@ struct ipv6_devconf {
         __s32           dad_transmits;
         __s32           rtr_solicits;
         __s32           rtr_solicit_interval;
+        __s32           rtr_solicit_max_interval;
         __s32           rtr_solicit_delay;
         __s32           force_mld_version;
         __s32           mldv1_unsolicited_report_interval;
diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index 9826d3a9464c..f2d072787947 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -1,8 +1,9 @@
 #ifndef _ADDRCONF_H
 #define _ADDRCONF_H
 
-#define MAX_RTR_SOLICITATIONS           3
+#define MAX_RTR_SOLICITATIONS           -1              /* unlimited */
 #define RTR_SOLICITATION_INTERVAL       (4*HZ)
+#define RTR_SOLICITATION_MAX_INTERVAL   (3600*HZ)       /* 1 hour */
 
 #define MIN_VALID_LIFETIME              (2*3600)        /* 2 hours */
 
diff --git a/include/net/if_inet6.h b/include/net/if_inet6.h
index 1c8b6820b694..515352c6280a 100644
--- a/include/net/if_inet6.h
+++ b/include/net/if_inet6.h
@@ -201,6 +201,7 @@ struct inet6_dev {
         struct ipv6_devstat     stats;
 
         struct timer_list       rs_timer;
+        __s32                   rs_interval;    /* in jiffies */
         __u8                    rs_probes;
 
         __u8                    addr_gen_mode;
diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index 395876060f50..8c2772340c3f 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -177,6 +177,7 @@ enum {
         DEVCONF_DROP_UNICAST_IN_L2_MULTICAST,
         DEVCONF_DROP_UNSOLICITED_NA,
         DEVCONF_KEEP_ADDR_ON_DOWN,
+        DEVCONF_RTR_SOLICIT_MAX_INTERVAL,
         DEVCONF_MAX
 };
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 35d4baa55c9d..87183983724d 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -112,6 +112,27 @@ static inline u32 cstamp_delta(unsigned long cstamp)
         return (cstamp - INITIAL_JIFFIES) * 100UL / HZ;
 }
 
+static inline s32 rfc3315_s14_backoff_init(s32 irt)
+{
+        /* multiply 'initial retransmission time' by 0.9 .. 1.1 */
+        u64 tmp = (900000 + prandom_u32() % 200001) * (u64)irt;
+        do_div(tmp, 1000000);
+        return (s32)tmp;
+}
+
+static inline s32 rfc3315_s14_backoff_update(s32 rt, s32 mrt)
+{
+        /* multiply 'retransmission timeout' by 1.9 .. 2.1 */
+        u64 tmp = (1900000 + prandom_u32() % 200001) * (u64)rt;
+        do_div(tmp, 1000000);
+        if ((s32)tmp > mrt) {
+                /* multiply 'maximum retransmission time' by 0.9 .. 1.1 */
+                tmp = (900000 + prandom_u32() % 200001) * (u64)mrt;
+                do_div(tmp, 1000000);
+        }
+        return (s32)tmp;
+}
+
 #ifdef CONFIG_SYSCTL
 static int addrconf_sysctl_register(struct inet6_dev *idev);
 static void addrconf_sysctl_unregister(struct inet6_dev *idev);
@@ -187,6 +208,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
         .dad_transmits          = 1,
         .rtr_solicits           = MAX_RTR_SOLICITATIONS,
         .rtr_solicit_interval   = RTR_SOLICITATION_INTERVAL,
+        .rtr_solicit_max_interval = RTR_SOLICITATION_MAX_INTERVAL,
         .rtr_solicit_delay      = MAX_RTR_SOLICITATION_DELAY,
         .use_tempaddr           = 0,
         .temp_valid_lft         = TEMP_VALID_LIFETIME,
@@ -232,6 +254,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
         .dad_transmits          = 1,
         .rtr_solicits           = MAX_RTR_SOLICITATIONS,
         .rtr_solicit_interval   = RTR_SOLICITATION_INTERVAL,
+        .rtr_solicit_max_interval = RTR_SOLICITATION_MAX_INTERVAL,
         .rtr_solicit_delay      = MAX_RTR_SOLICITATION_DELAY,
         .use_tempaddr           = 0,
         .temp_valid_lft         = TEMP_VALID_LIFETIME,
@@ -3687,7 +3710,7 @@ static void addrconf_rs_timer(unsigned long data)
         if (idev->if_flags & IF_RA_RCVD)
                 goto out;
 
-        if (idev->rs_probes++ < idev->cnf.rtr_solicits) {
+        if (idev->rs_probes++ < idev->cnf.rtr_solicits || idev->cnf.rtr_solicits < 0) {
                 write_unlock(&idev->lock);
                 if (!ipv6_get_lladdr(dev, &lladdr, IFA_F_TENTATIVE))
                         ndisc_send_rs(dev, &lladdr,
@@ -3696,11 +3719,13 @@ static void addrconf_rs_timer(unsigned long data)
                         goto put;
 
                 write_lock(&idev->lock);
+                idev->rs_interval = rfc3315_s14_backoff_update(
+                        idev->rs_interval, idev->cnf.rtr_solicit_max_interval);
                 /* The wait after the last probe can be shorter */
                 addrconf_mod_rs_timer(idev, (idev->rs_probes ==
                                              idev->cnf.rtr_solicits) ?
                                       idev->cnf.rtr_solicit_delay :
-                                      idev->cnf.rtr_solicit_interval);
+                                      idev->rs_interval);
         } else {
                 /*
                  * Note: we do not support deprecated "all on-link"
@@ -3949,7 +3974,7 @@ static void addrconf_dad_completed(struct inet6_ifaddr *ifp)
         send_mld = ifp->scope == IFA_LINK && ipv6_lonely_lladdr(ifp);
         send_rs = send_mld &&
                   ipv6_accept_ra(ifp->idev) &&
-                  ifp->idev->cnf.rtr_solicits > 0 &&
+                  ifp->idev->cnf.rtr_solicits != 0 &&
                   (dev->flags&IFF_LOOPBACK) == 0;
         read_unlock_bh(&ifp->idev->lock);
 
@@ -3971,10 +3996,11 @@ static void addrconf_dad_completed(struct inet6_ifaddr *ifp)
 
                 write_lock_bh(&ifp->idev->lock);
                 spin_lock(&ifp->lock);
+                ifp->idev->rs_interval = rfc3315_s14_backoff_init(
+                        ifp->idev->cnf.rtr_solicit_interval);
                 ifp->idev->rs_probes = 1;
                 ifp->idev->if_flags |= IF_RS_SENT;
-                addrconf_mod_rs_timer(ifp->idev,
-                                      ifp->idev->cnf.rtr_solicit_interval);
+                addrconf_mod_rs_timer(ifp->idev, ifp->idev->rs_interval);
                 spin_unlock(&ifp->lock);
                 write_unlock_bh(&ifp->idev->lock);
         }
@@ -4891,6 +4917,8 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
         array[DEVCONF_RTR_SOLICITS] = cnf->rtr_solicits;
         array[DEVCONF_RTR_SOLICIT_INTERVAL] =
                 jiffies_to_msecs(cnf->rtr_solicit_interval);
+        array[DEVCONF_RTR_SOLICIT_MAX_INTERVAL] =
+                jiffies_to_msecs(cnf->rtr_solicit_max_interval);
         array[DEVCONF_RTR_SOLICIT_DELAY] =
                 jiffies_to_msecs(cnf->rtr_solicit_delay);
         array[DEVCONF_FORCE_MLD_VERSION] = cnf->force_mld_version;
@@ -5099,7 +5127,7 @@ static int inet6_set_iftoken(struct inet6_dev *idev, struct in6_addr *token)
                 return -EINVAL;
         if (!ipv6_accept_ra(idev))
                 return -EINVAL;
-        if (idev->cnf.rtr_solicits <= 0)
+        if (idev->cnf.rtr_solicits == 0)
                 return -EINVAL;
 
         write_lock_bh(&idev->lock);
@@ -5128,8 +5156,10 @@ update_lft:
 
         if (update_rs) {
                 idev->if_flags |= IF_RS_SENT;
+                idev->rs_interval = rfc3315_s14_backoff_init(
+                        idev->cnf.rtr_solicit_interval);
                 idev->rs_probes = 1;
-                addrconf_mod_rs_timer(idev, idev->cnf.rtr_solicit_interval);
+                addrconf_mod_rs_timer(idev, idev->rs_interval);
         }
 
         /* Well, that's kinda nasty ... */
@@ -5778,6 +5808,13 @@ static const struct ctl_table addrconf_sysctl[] = {
                 .proc_handler   = proc_dointvec_jiffies,
         },
         {
+                .procname       = "router_solicitation_max_interval",
+                .data           = &ipv6_devconf.rtr_solicit_max_interval,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = proc_dointvec_jiffies,
+        },
+        {
                 .procname       = "router_solicitation_delay",
                 .data           = &ipv6_devconf.rtr_solicit_delay,
                 .maxlen         = sizeof(int),