From 3e8e2f0a6590a3b1eeb989e364fe4b5638be108f Mon Sep 17 00:00:00 2001
From: Phil Sutter <phil@nwl.cc>
Date: Tue, 15 Dec 2020 15:40:56 +0100
Subject: [PATCH] libxtables: Implement notargets hash table

Target lookup is relatively costly due to the filesystem access. Avoid
this overhead in huge rulesets which contain many chain jumps by caching
the failed lookups into a hashtable for later.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Acked-by: Florian Westphal <fw@strlen.de>
(cherry picked from commit f58b0d7406451afbb4b9b6c7888990c964fa7c79)

Conflicts:
	libxtables/xtables.c
-> Context changes and missing xtables_fini() due to missing commit
   7db4333dc0b6c ("libxtables: Introduce xtables_fini()")
---
 libxtables/xtables.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/libxtables/xtables.c b/libxtables/xtables.c
index 58dd69440253d..1e1c218df7441 100644
--- a/libxtables/xtables.c
+++ b/libxtables/xtables.c
@@ -48,6 +48,7 @@
 #include <linux/netfilter_ipv4/ip_tables.h>
 #include <linux/netfilter_ipv6/ip6_tables.h>
 #include <libiptc/libxtc.h>
+#include <libiptc/linux_list.h>
 
 #ifndef NO_SHARED_LIBS
 #include <dlfcn.h>
@@ -208,6 +209,71 @@ static bool xtables_fully_register_pending_match(struct xtables_match *me,
 static bool xtables_fully_register_pending_target(struct xtables_target *me,
 						  struct xtables_target *prev);
 
+struct notarget {
+	struct hlist_node node;
+	char name[];
+};
+
+#define NOTARGET_HSIZE	512
+static struct hlist_head notargets[NOTARGET_HSIZE];
+
+static void notargets_hlist_init(void)
+{
+	int i;
+
+	for (i = 0; i < NOTARGET_HSIZE; i++)
+		INIT_HLIST_HEAD(&notargets[i]);
+}
+
+static void notargets_hlist_free(void)
+{
+	struct hlist_node *pos, *n;
+	struct notarget *cur;
+	int i;
+
+	for (i = 0; i < NOTARGET_HSIZE; i++) {
+		hlist_for_each_entry_safe(cur, pos, n, &notargets[i], node) {
+			hlist_del(&cur->node);
+			free(cur);
+		}
+	}
+}
+
+static uint32_t djb_hash(const char *key)
+{
+	uint32_t i, hash = 5381;
+
+	for (i = 0; i < strlen(key); i++)
+		hash = ((hash << 5) + hash) + key[i];
+
+	return hash;
+}
+
+static struct notarget *notargets_hlist_lookup(const char *name)
+{
+	uint32_t key = djb_hash(name) % NOTARGET_HSIZE;
+	struct hlist_node *node;
+	struct notarget *cur;
+
+	hlist_for_each_entry(cur, node, &notargets[key], node) {
+		if (!strcmp(name, cur->name))
+			return cur;
+	}
+	return NULL;
+}
+
+static void notargets_hlist_insert(const char *name)
+{
+	struct notarget *cur;
+
+	if (!name)
+		return;
+
+	cur = xtables_malloc(sizeof(*cur) + strlen(name) + 1);
+	strcpy(cur->name, name);
+	hlist_add_head(&cur->node, &notargets[djb_hash(name) % NOTARGET_HSIZE]);
+}
+
 void xtables_init(void)
 {
 	xtables_libdir = getenv("XTABLES_LIBDIR");
@@ -233,6 +299,13 @@ void xtables_init(void)
 		return;
 	}
 	xtables_libdir = XTABLES_LIBDIR;
+
+	notargets_hlist_init();
+}
+
+void xtables_fini(void)
+{
+	notargets_hlist_free();
 }
 
 void xtables_set_nfproto(uint8_t nfproto)
@@ -750,6 +823,10 @@ xtables_find_target(const char *name, enum xtables_tryload tryload)
 	    || strcmp(name, XTC_LABEL_QUEUE) == 0
 	    || strcmp(name, XTC_LABEL_RETURN) == 0)
 		name = "standard";
+	/* known non-target? */
+	else if (notargets_hlist_lookup(name) &&
+		 tryload != XTF_LOAD_MUST_SUCCEED)
+		return NULL;
 
 	/* Trigger delayed initialization */
 	for (dptr = &xtables_pending_targets; *dptr; ) {
@@ -813,6 +890,8 @@ xtables_find_target(const char *name, enum xtables_tryload tryload)
 
 	if (ptr)
 		ptr->used = 1;
+	else
+		notargets_hlist_insert(name);
 
 	return ptr;
 }
-- 
2.34.1