neighbour: fix base_reachable_time(_ms) not effective immediatly when changed

When setting base_reachable_time or base_reachable_time_ms on a
specific interface through sysctl or netlink, the reachable_time
value is not updated.

This means that neighbour entries will continue to be updated using the
old value until it is recomputed in neigh_period_work (which
    recomputes the value every 300*HZ).
On systems with HZ equal to 1000 for instance, it means 5mins before
the change is effective.

This patch changes this behavior by recomputing reachable_time after
each set on base_reachable_time or base_reachable_time_ms.
The new value will become effective the next time the neighbour's timer
is triggered.

Changes are made in two places: the netlink code for set and the sysctl
handling code. For sysctl, I use a proc_handler. The ipv6 network
code does provide its own handler but it already refreshes
reachable_time correctly so it's not an issue.
Any other user of neighbour which provide its own handlers must
refresh reachable_time.

Signed-off-by: Jean-Francois Remy <jeff@melix.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 44 insertions, 0 deletions

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 8e38f17288d3..8d614c93f86a 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2043,6 +2043,12 @@ static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh)
                         case NDTPA_BASE_REACHABLE_TIME:
                                 NEIGH_VAR_SET(p, BASE_REACHABLE_TIME,
                                               nla_get_msecs(tbp[i]));
+                                /* update reachable_time as well, otherwise, the change will
+                                 * only be effective after the next time neigh_periodic_work
+                                 * decides to recompute it (can be multiple minutes)
+                                 */
+                                p->reachable_time =
+                                        neigh_rand_reach_time(NEIGH_VAR(p, BASE_REACHABLE_TIME));
                                 break;
                         case NDTPA_GC_STALETIME:
                                 NEIGH_VAR_SET(p, GC_STALETIME,
@@ -2921,6 +2927,31 @@ static int neigh_proc_dointvec_unres_qlen(struct ctl_table *ctl, int write,
         return ret;
 }
 
+static int neigh_proc_base_reachable_time(struct ctl_table *ctl, int write,
+                                          void __user *buffer,
+                                          size_t *lenp, loff_t *ppos)
+{
+        struct neigh_parms *p = ctl->extra2;
+        int ret;
+
+        if (strcmp(ctl->procname, "base_reachable_time") == 0)
+                ret = neigh_proc_dointvec_jiffies(ctl, write, buffer, lenp, ppos);
+        else if (strcmp(ctl->procname, "base_reachable_time_ms") == 0)
+                ret = neigh_proc_dointvec_ms_jiffies(ctl, write, buffer, lenp, ppos);
+        else
+                ret = -1;
+
+        if (write && ret == 0) {
+                /* update reachable_time as well, otherwise, the change will
+                 * only be effective after the next time neigh_periodic_work
+                 * decides to recompute it
+                 */
+                p->reachable_time =
+                        neigh_rand_reach_time(NEIGH_VAR(p, BASE_REACHABLE_TIME));
+        }
+        return ret;
+}
+
 #define NEIGH_PARMS_DATA_OFFSET(index)  \
         (&((struct neigh_parms *) 0)->data[index])
 
@@ -3047,6 +3078,19 @@ int neigh_sysctl_register(struct net_device *dev, struct neigh_parms *p,
                 t->neigh_vars[NEIGH_VAR_RETRANS_TIME_MS].proc_handler = handler;
                 /* ReachableTime (in milliseconds) */
                 t->neigh_vars[NEIGH_VAR_BASE_REACHABLE_TIME_MS].proc_handler = handler;
+        } else {
+                /* Those handlers will update p->reachable_time after
+                 * base_reachable_time(_ms) is set to ensure the new timer starts being
+                 * applied after the next neighbour update instead of waiting for
+                 * neigh_periodic_work to update its value (can be multiple minutes)
+                 * So any handler that replaces them should do this as well
+                 */
+                /* ReachableTime */
+                t->neigh_vars[NEIGH_VAR_BASE_REACHABLE_TIME].proc_handler =
+                        neigh_proc_base_reachable_time;
+                /* ReachableTime (in milliseconds) */
+                t->neigh_vars[NEIGH_VAR_BASE_REACHABLE_TIME_MS].proc_handler =
+                        neigh_proc_base_reachable_time;
         }
 
         /* Don't export sysctls to unprivileged users */