net: neigh: decrement the family specific qlen
Commit Message
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>
---
include/net/neighbour.h | 2 +-
net/core/neighbour.c | 58 +++++++++++++++++++++--------------------
2 files changed, 31 insertions(+), 29 deletions(-)
Comments
Hello,
On Sat, 2022-11-12 at 11:48 +0100, Thomas Zeitlhofer wrote:
> 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>
> ---
> include/net/neighbour.h | 2 +-
> net/core/neighbour.c | 58 +++++++++++++++++++++--------------------
> 2 files changed, 31 insertions(+), 29 deletions(-)
>
> diff --git a/include/net/neighbour.h b/include/net/neighbour.h
> index 20745cf7ae1a..cc0b65b7c829 100644
> --- 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);
> };
The patch LGTM, but why did you use __u32 above? this is not part of
uAPI, plain u32 should be fine.
Thanks!
Paolo
@@ -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);
};
@@ -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)
{