netfilter: xt_recent: add an entry reaper

One of the problems with the way xt_recent is implemented is that
there is no efficient way to remove expired entries. Of course,
one can write a rule '-m recent --remove', but you have to know
beforehand which entry to delete. This commit adds reaper
logic which checks the head of the LRU list when a rule
is invoked that has a '--seconds' value and XT_RECENT_REAP set. If an
entry ceases to accumulate time stamps, then it will eventually bubble
to the top of the LRU list where it is then reaped.

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

2 files changed, 31 insertions, 1 deletions

diff --git a/include/linux/netfilter/xt_recent.h b/include/linux/netfilter/xt_recent.h
index d2c276609925..bba990ecb018 100644
--- a/include/linux/netfilter/xt_recent.h
+++ b/include/linux/netfilter/xt_recent.h
@@ -9,6 +9,7 @@ enum {
         XT_RECENT_UPDATE   = 1 << 2,
         XT_RECENT_REMOVE   = 1 << 3,
         XT_RECENT_TTL      = 1 << 4,
+        XT_RECENT_REAP     = 1 << 5,
 
         XT_RECENT_SOURCE   = 0,
         XT_RECENT_DEST     = 1,
@@ -16,6 +17,9 @@ enum {
         XT_RECENT_NAME_LEN = 200,
 };
 
+/* Only allowed with --rcheck and --update */
+#define XT_RECENT_MODIFIERS (XT_RECENT_TTL|XT_RECENT_REAP)
+
 struct xt_recent_mtinfo {
         __u32 seconds;
         __u32 hit_count;
diff --git a/net/netfilter/xt_recent.c b/net/netfilter/xt_recent.c
index 2ff8aae84a38..b65eca9e13a3 100644
--- a/net/netfilter/xt_recent.c
+++ b/net/netfilter/xt_recent.c
@@ -143,6 +143,25 @@ static void recent_entry_remove(struct recent_table *t, struct recent_entry *e)
         t->entries--;
 }
 
+/*
+ * Drop entries with timestamps older then 'time'.
+ */
+static void recent_entry_reap(struct recent_table *t, unsigned long time)
+{
+        struct recent_entry *e;
+
+        /*
+         * The head of the LRU list is always the oldest entry.
+         */
+        e = list_entry(t->lru_list.next, struct recent_entry, lru_list);
+
+        /*
+         * The last time stamp is the most recent.
+         */
+        if (time_after(time, e->stamps[e->index-1]))
+                recent_entry_remove(t, e);
+}
+
 static struct recent_entry *
 recent_entry_init(struct recent_table *t, const union nf_inet_addr *addr,
                   u_int16_t family, u_int8_t ttl)
@@ -269,6 +288,10 @@ recent_mt(const struct sk_buff *skb, const struct xt_match_param *par)
                                 break;
                         }
                 }
+
+                /* info->seconds must be non-zero */
+                if (info->check_set & XT_RECENT_REAP)
+                        recent_entry_reap(t, time);
         }
 
         if (info->check_set & XT_RECENT_SET ||
@@ -301,7 +324,10 @@ static bool recent_mt_check(const struct xt_mtchk_param *par)
                       XT_RECENT_CHECK | XT_RECENT_UPDATE)) != 1)
                 return false;
         if ((info->check_set & (XT_RECENT_SET | XT_RECENT_REMOVE)) &&
-            (info->seconds || info->hit_count))
+            (info->seconds || info->hit_count ||
+            (info->check_set & XT_RECENT_MODIFIERS)))
+                return false;
+        if ((info->check_set & XT_RECENT_REAP) && !info->seconds)
                 return false;
         if (info->hit_count > ip_pkt_list_tot) {
                 pr_info(KBUILD_MODNAME ": hitcount (%u) is larger than "