net: neigh: decrement the family specific qlen

Commit 0ff4eb3d5ebb ("neighbour: make proxy_queue.qlen limit
per-device") introduced the length counter qlen in struct neigh_parms.
There are separate neigh_parms instances for IPv4/ARP and IPv6/ND, and
while the family specific qlen is incremented in pneigh_enqueue(), the
mentioned commit decrements always the IPv4/ARP specific qlen,
regardless of the currently processed family, in pneigh_queue_purge()
and neigh_proxy_process().

As a result, with IPv6/ND, the family specific qlen is only incremented
(and never decremented) until it exceeds PROXY_QLEN, and then, according
to the check in pneigh_enqueue(), neighbor solicitations are not
answered anymore. As an example, this is noted when using the
subnet-router anycast address to access a Linux router. After a certain
amount of time (in the observed case, qlen exceeded PROXY_QLEN after two
days), the Linux router stops answering neighbor solicitations for its
subnet-router anycast address and effectively becomes unreachable.

Another result with IPv6/ND is that the IPv4/ARP specific qlen is
decremented more often than incremented. This leads to negative qlen
values, as a signed integer has been used for the length counter qlen,
and potentially to an integer overflow.

Fix this by introducing the helper function neigh_parms_qlen_dec(),
which decrements the family specific qlen. Thereby, make use of the
existing helper function neigh_get_dev_parms_rcu(), whose definition
therefore needs to be placed earlier in neighbour.c. Take the family
member from struct neigh_table to determine the currently processed
family and appropriately call neigh_parms_qlen_dec() from
pneigh_queue_purge() and neigh_proxy_process().

Additionally, use an unsigned integer for the length counter qlen.

Fixes: 0ff4eb3d5ebb ("neighbour: make proxy_queue.qlen limit per-device")
Signed-off-by: Thomas Zeitlhofer <thomas.zeitlhofer+lkml@ze-it.at>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 20745cf..2f2a602 100644 (file)
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -83,7 +83,7 @@ struct neigh_parms {
        struct rcu_head rcu_head;
 
        int     reachable_time;
-       int     qlen;
+       u32     qlen;
        int     data[NEIGH_VAR_DATA_MAX];
        DECLARE_BITMAP(data_state, NEIGH_VAR_DATA_MAX);
 };

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index a77a85e..952a547 100644 (file)
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -307,7 +307,31 @@ static int neigh_del_timer(struct neighbour *n)
        return 0;
 }
 
-static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net)
+static struct neigh_parms *neigh_get_dev_parms_rcu(struct net_device *dev,
+                                                  int family)
+{
+       switch (family) {
+       case AF_INET:
+               return __in_dev_arp_parms_get_rcu(dev);
+       case AF_INET6:
+               return __in6_dev_nd_parms_get_rcu(dev);
+       }
+       return NULL;
+}
+
+static void neigh_parms_qlen_dec(struct net_device *dev, int family)
+{
+       struct neigh_parms *p;
+
+       rcu_read_lock();
+       p = neigh_get_dev_parms_rcu(dev, family);
+       if (p)
+               p->qlen--;
+       rcu_read_unlock();
+}
+
+static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net,
+                              int family)
 {
        struct sk_buff_head tmp;
        unsigned long flags;
@@ -321,13 +345,7 @@ static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net)
                struct net_device *dev = skb->dev;
 
                if (net == NULL || net_eq(dev_net(dev), net)) {
-                       struct in_device *in_dev;
-
-                       rcu_read_lock();
-                       in_dev = __in_dev_get_rcu(dev);
-                       if (in_dev)
-                               in_dev->arp_parms->qlen--;
-                       rcu_read_unlock();
+                       neigh_parms_qlen_dec(dev, family);
                        __skb_unlink(skb, list);
                        __skb_queue_tail(&tmp, skb);
                }
@@ -409,7 +427,8 @@ static int __neigh_ifdown(struct neigh_table *tbl, struct net_device *dev,
        write_lock_bh(&tbl->lock);
        neigh_flush_dev(tbl, dev, skip_perm);
        pneigh_ifdown_and_unlock(tbl, dev);
-       pneigh_queue_purge(&tbl->proxy_queue, dev ? dev_net(dev) : NULL);
+       pneigh_queue_purge(&tbl->proxy_queue, dev ? dev_net(dev) : NULL,
+                          tbl->family);
        if (skb_queue_empty_lockless(&tbl->proxy_queue))
                del_timer_sync(&tbl->proxy_timer);
        return 0;
@@ -1621,13 +1640,8 @@ static void neigh_proxy_process(struct timer_list *t)
 
                if (tdif <= 0) {
                        struct net_device *dev = skb->dev;
-                       struct in_device *in_dev;
 
-                       rcu_read_lock();
-                       in_dev = __in_dev_get_rcu(dev);
-                       if (in_dev)
-                               in_dev->arp_parms->qlen--;
-                       rcu_read_unlock();
+                       neigh_parms_qlen_dec(dev, tbl->family);
                        __skb_unlink(skb, &tbl->proxy_queue);
 
                        if (tbl->proxy_redo && netif_running(dev)) {
@@ -1821,7 +1835,7 @@ int neigh_table_clear(int index, struct neigh_table *tbl)
        cancel_delayed_work_sync(&tbl->managed_work);
        cancel_delayed_work_sync(&tbl->gc_work);
        del_timer_sync(&tbl->proxy_timer);
-       pneigh_queue_purge(&tbl->proxy_queue, NULL);
+       pneigh_queue_purge(&tbl->proxy_queue, NULL, tbl->family);
        neigh_ifdown(tbl, NULL);
        if (atomic_read(&tbl->entries))
                pr_crit("neighbour leakage\n");
@@ -3539,18 +3553,6 @@ static int proc_unres_qlen(struct ctl_table *ctl, int write,
        return ret;
 }
 
-static struct neigh_parms *neigh_get_dev_parms_rcu(struct net_device *dev,
-                                                  int family)
-{
-       switch (family) {
-       case AF_INET:
-               return __in_dev_arp_parms_get_rcu(dev);
-       case AF_INET6:
-               return __in6_dev_nd_parms_get_rcu(dev);
-       }
-       return NULL;
-}
-
 static void neigh_copy_dflt_parms(struct net *net, struct neigh_parms *p,
                                  int index)
 {