[PATCH] [NETNS49] support for per/namespace routing cache cleanup

["Denis V. Lunev" <den-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

/proc/sys/net/route/flush should be accessible inside the net namespace.
Though, the complete opening of this file will result in a DoS or
significant entire host slowdown if a namespace process will continually
flush routes.

This patch introduces per/namespace route flush facility.

Each namespace wanted to flush a cache copies global generation count to
itself and starts the timer. The cache is dropped for a specific namespace
iff the namespace counter is greater or equal global ones.

So, in general, unwanted namespaces do nothing. They hold very old low
counter and they are unaffected by the requested cleanup.

Signed-of-by: Denis V. Lunev <den-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 85abf14..b492ce8 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -143,6 +143,8 @@ struct net {
 
 	/* iptable_filter.c */
 	struct xt_table		*ip_packet_filter;
+
+	unsigned long		rt_flush_required;
 };
 
 extern struct net init_net;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f9a59ff..413587c 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -91,6 +91,7 @@
 #include <linux/jhash.h>
 #include <linux/rcupdate.h>
 #include <linux/times.h>
+#include <linux/nsproxy.h>
 #include <net/net_namespace.h>
 #include <net/protocol.h>
 #include <net/ip.h>
@@ -642,6 +643,51 @@ static void rt_check_expire(unsigned long dummy)
 	mod_timer(&rt_periodic_timer, jiffies + ip_rt_gc_interval);
 }
 
+
+static DEFINE_SPINLOCK(rt_flush_lock);
+
+#ifdef CONFIG_NET_NS
+static unsigned long rt_flush_gen;
+
+/* called under rt_flush_lock */
+static void rt_flush_required_set(struct net *net)
+{
+	/*
+	 * If the global generation rt_flush_gen is equal to G, then
+	 * the pass considering entries labelled by G is yet to come.
+	 */
+	net->rt_flush_required = rt_flush_gen;
+}
+
+static unsigned long rt_flush_required_reset(void)
+{
+	unsigned long g;
+
+	spin_lock_bh(&rt_flush_lock);
+	g = rt_flush_gen++;
+	spin_unlock_bh(&rt_flush_lock);
+	return g;
+}
+
+static int rt_flush_required_check(struct net *net, unsigned long gen)
+{
+	/* can be checked without the lock */
+	return net->rt_flush_required >= gen;
+}
+
+#else
+
+static void rt_flush_required_reset(struct net *net)
+{
+}
+
+static unsigned long rt_flush_required_reset(void)
+{
+	return 0;
+}
+#endif
+
+
 /* This can run from both BH and non-BH contexts, the latter
  * in the case of a forced flush event.
  */
@@ -649,16 +695,46 @@ static void rt_run_flush(unsigned long dummy)
 {
 	int i;
 	struct rtable *rth, *next;
+	unsigned long gen;
 
 	rt_deadline = 0;
 
 	get_random_bytes(&rt_hash_rnd, 4);
+	gen = rt_flush_required_reset();
 
 	for (i = rt_hash_mask; i >= 0; i--) {
+#ifdef CONFIG_NET_NS
+		struct rtable **prev, *p, *tail;
+
+		spin_lock_bh(rt_hash_lock_addr(i));
+		rth = rt_hash_table[i].chain;
+
+		/* defer releasing the head of the list after spin_unlock */
+		for (tail = rth; tail; tail = tail->u.dst.rt_next)
+			if (!rt_flush_required_check(tail->fl.fl_net, gen))
+				break;
+		if (rth != tail)
+			rt_hash_table[i].chain = tail;
+
+		/* call rt_free on entries after the tail requiring flush */
+		prev = &rt_hash_table[i].chain;
+		for (p = *prev; p; p = next) {
+			next = p->u.dst.rt_next;
+			if (!rt_flush_required_check(p->fl.fl_net, gen)) {
+				prev = &p->u.dst.rt_next;
+			} else {
+				*prev = next;
+				rt_free(p);
+			}
+		}
+#else
 		spin_lock_bh(rt_hash_lock_addr(i));
 		rth = rt_hash_table[i].chain;
 		if (rth)
 			rt_hash_table[i].chain = NULL;
+		tail = NULL;
+
+#endif
 		spin_unlock_bh(rt_hash_lock_addr(i));
 
 		for (; rth; rth = next) {
@@ -668,8 +744,6 @@ static void rt_run_flush(unsigned long dummy)
 	}
 }
 
-static DEFINE_SPINLOCK(rt_flush_lock);
-
 void rt_cache_flush(int delay)
 {
 	unsigned long now = jiffies;
@@ -697,6 +771,8 @@ void rt_cache_flush(int delay)
 			delay = tmo;
 	}
 
+	rt_flush_required_set(current->nsproxy->net_ns);
+
 	if (delay <= 0) {
 		spin_unlock_bh(&rt_flush_lock);
 		rt_run_flush(0);