netfilter: x_tables: speed up jump target validation

The dummy ruleset I used to test the original validation change was broken,
most rules were unreachable and were not tested by mark_source_chains().

In some cases rulesets that used to load in a few seconds now require
several minutes.

sample ruleset that shows the behaviour:

echo "*filter"
for i in $(seq 0 100000);do
printf ":chain_%06x - [0:0]\n" $i
done
for i in $(seq 0 100000);do
printf -- "-A INPUT -j chain_%06x\n" $i
printf -- "-A INPUT -j chain_%06x\n" $i
printf -- "-A INPUT -j chain_%06x\n" $i
done
echo COMMIT

[ pipe result into iptables-restore ]

This ruleset will be about 74mbyte in size, with ~500k searches
though all 500k[1] rule entries. iptables-restore will take forever
(gave up after 10 minutes)

Instead of always searching the entire blob for a match, fill an
array with the start offsets of every single ipt_entry struct,
then do a binary search to check if the jump target is present or not.

After this change ruleset restore times get again close to what one
gets when reverting 36472341017529e (~3 seconds on my workstation).

[1] every user-defined rule gets an implicit RETURN, so we get
300k jumps + 100k userchains + 100k returns -> 500k rule entries

Fixes: 36472341017529e ("netfilter: x_tables: validate targets of jumps")
Reported-by: Jeff Wu <[e-mail]>
Tested-by: Jeff Wu <[e-mail]>
Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter/x_tables.h

···
 			   unsigned int target_offset,
 			   unsigned int next_offset);
 
+unsigned int *xt_alloc_entry_offsets(unsigned int size);
+bool xt_find_jump_offset(const unsigned int *offsets,
+			 unsigned int target, unsigned int size);
+
 int xt_check_match(struct xt_mtchk_param *, unsigned int size, u_int8_t proto,
 		   bool inv_proto);
 int xt_check_target(struct xt_tgchk_param *, unsigned int size, u_int8_t proto,

net/ipv4/netfilter/arp_tables.c

···
 	       memcmp(&e->arp, &uncond, sizeof(uncond)) == 0;
 }
 
-static bool find_jump_target(const struct xt_table_info *t,
-			     const struct arpt_entry *target)
-{
-	struct arpt_entry *iter;
-
-	xt_entry_foreach(iter, t->entries, t->size) {
-		 if (iter == target)
-			return true;
-	}
-	return false;
-}
-
 /* Figures out from what hook each rule can be called: returns 0 if
  * there are loops.  Puts hook bitmask in comefrom.
  */
 static int mark_source_chains(const struct xt_table_info *newinfo,
-			      unsigned int valid_hooks, void *entry0)
+			      unsigned int valid_hooks, void *entry0,
+			      unsigned int *offsets)
 {
 	unsigned int hook;
 
···
 					   XT_STANDARD_TARGET) == 0 &&
 				    newpos >= 0) {
 					/* This a jump; chase it. */
+					if (!xt_find_jump_offset(offsets, newpos,
+								 newinfo->number))
+						return 0;
 					e = (struct arpt_entry *)
 						(entry0 + newpos);
-					if (!find_jump_target(newinfo, e))
-						return 0;
 				} else {
 					/* ... this is a fallthru */
 					newpos = pos + e->next_offset;
···
 			   const struct arpt_replace *repl)
 {
 	struct arpt_entry *iter;
+	unsigned int *offsets;
 	unsigned int i;
 	int ret = 0;
 
···
 		newinfo->underflow[i] = 0xFFFFFFFF;
 	}
 
+	offsets = xt_alloc_entry_offsets(newinfo->number);
+	if (!offsets)
+		return -ENOMEM;
 	i = 0;
 
 	/* Walk through entries, checking offsets. */
···
 						 repl->underflow,
 						 repl->valid_hooks);
 		if (ret != 0)
-			break;
+			goto out_free;
+		if (i < repl->num_entries)
+			offsets[i] = (void *)iter - entry0;
 		++i;
 		if (strcmp(arpt_get_target(iter)->u.user.name,
 		    XT_ERROR_TARGET) == 0)
 			++newinfo->stacksize;
 	}
 	if (ret != 0)
-		return ret;
+		goto out_free;
 
+	ret = -EINVAL;
 	if (i != repl->num_entries)
-		return -EINVAL;
+		goto out_free;
 
 	/* Check hooks all assigned */
 	for (i = 0; i < NF_ARP_NUMHOOKS; i++) {
···
 		if (!(repl->valid_hooks & (1 << i)))
 			continue;
 		if (newinfo->hook_entry[i] == 0xFFFFFFFF)
-			return -EINVAL;
+			goto out_free;
 		if (newinfo->underflow[i] == 0xFFFFFFFF)
-			return -EINVAL;
+			goto out_free;
 	}
 
-	if (!mark_source_chains(newinfo, repl->valid_hooks, entry0))
-		return -ELOOP;
+	if (!mark_source_chains(newinfo, repl->valid_hooks, entry0, offsets)) {
+		ret = -ELOOP;
+		goto out_free;
+	}
+	kvfree(offsets);
 
 	/* Finally, each sanity check must pass */
 	i = 0;
···
 		return ret;
 	}
 
+	return ret;
+ out_free:
+	kvfree(offsets);
 	return ret;
 }
 

net/ipv4/netfilter/ip_tables.c

···
 	else return verdict;
 }
 
-static bool find_jump_target(const struct xt_table_info *t,
-			     const struct ipt_entry *target)
-{
-	struct ipt_entry *iter;
-
-	xt_entry_foreach(iter, t->entries, t->size) {
-		 if (iter == target)
-			return true;
-	}
-	return false;
-}
-
 /* Figures out from what hook each rule can be called: returns 0 if
    there are loops.  Puts hook bitmask in comefrom. */
 static int
 mark_source_chains(const struct xt_table_info *newinfo,
-		   unsigned int valid_hooks, void *entry0)
+		   unsigned int valid_hooks, void *entry0,
+		   unsigned int *offsets)
 {
 	unsigned int hook;
 
···
 					   XT_STANDARD_TARGET) == 0 &&
 				    newpos >= 0) {
 					/* This a jump; chase it. */
+					if (!xt_find_jump_offset(offsets, newpos,
+								 newinfo->number))
+						return 0;
 					e = (struct ipt_entry *)
 						(entry0 + newpos);
-					if (!find_jump_target(newinfo, e))
-						return 0;
 				} else {
 					/* ... this is a fallthru */
 					newpos = pos + e->next_offset;
···
 		const struct ipt_replace *repl)
 {
 	struct ipt_entry *iter;
+	unsigned int *offsets;
 	unsigned int i;
 	int ret = 0;
 
···
 		newinfo->underflow[i] = 0xFFFFFFFF;
 	}
 
+	offsets = xt_alloc_entry_offsets(newinfo->number);
+	if (!offsets)
+		return -ENOMEM;
 	i = 0;
 	/* Walk through entries, checking offsets. */
 	xt_entry_foreach(iter, entry0, newinfo->size) {
···
 						 repl->underflow,
 						 repl->valid_hooks);
 		if (ret != 0)
-			return ret;
+			goto out_free;
+		if (i < repl->num_entries)
+			offsets[i] = (void *)iter - entry0;
 		++i;
 		if (strcmp(ipt_get_target(iter)->u.user.name,
 		    XT_ERROR_TARGET) == 0)
 			++newinfo->stacksize;
 	}
 
+	ret = -EINVAL;
 	if (i != repl->num_entries)
-		return -EINVAL;
+		goto out_free;
 
 	/* Check hooks all assigned */
 	for (i = 0; i < NF_INET_NUMHOOKS; i++) {
···
 		if (!(repl->valid_hooks & (1 << i)))
 			continue;
 		if (newinfo->hook_entry[i] == 0xFFFFFFFF)
-			return -EINVAL;
+			goto out_free;
 		if (newinfo->underflow[i] == 0xFFFFFFFF)
-			return -EINVAL;
+			goto out_free;
 	}
 
-	if (!mark_source_chains(newinfo, repl->valid_hooks, entry0))
-		return -ELOOP;
+	if (!mark_source_chains(newinfo, repl->valid_hooks, entry0, offsets)) {
+		ret = -ELOOP;
+		goto out_free;
+	}
+	kvfree(offsets);
 
 	/* Finally, each sanity check must pass */
 	i = 0;
···
 		return ret;
 	}
 
+	return ret;
+ out_free:
+	kvfree(offsets);
 	return ret;
 }
 

net/ipv6/netfilter/ip6_tables.c

···
 	else return verdict;
 }
 
-static bool find_jump_target(const struct xt_table_info *t,
-			     const struct ip6t_entry *target)
-{
-	struct ip6t_entry *iter;
-
-	xt_entry_foreach(iter, t->entries, t->size) {
-		 if (iter == target)
-			return true;
-	}
-	return false;
-}
-
 /* Figures out from what hook each rule can be called: returns 0 if
    there are loops.  Puts hook bitmask in comefrom. */
 static int
 mark_source_chains(const struct xt_table_info *newinfo,
-		   unsigned int valid_hooks, void *entry0)
+		   unsigned int valid_hooks, void *entry0,
+		   unsigned int *offsets)
 {
 	unsigned int hook;
 
···
 					   XT_STANDARD_TARGET) == 0 &&
 				    newpos >= 0) {
 					/* This a jump; chase it. */
+					if (!xt_find_jump_offset(offsets, newpos,
+								 newinfo->number))
+						return 0;
 					e = (struct ip6t_entry *)
 						(entry0 + newpos);
-					if (!find_jump_target(newinfo, e))
-						return 0;
 				} else {
 					/* ... this is a fallthru */
 					newpos = pos + e->next_offset;
···
 		const struct ip6t_replace *repl)
 {
 	struct ip6t_entry *iter;
+	unsigned int *offsets;
 	unsigned int i;
 	int ret = 0;
 
···
 		newinfo->underflow[i] = 0xFFFFFFFF;
 	}
 
+	offsets = xt_alloc_entry_offsets(newinfo->number);
+	if (!offsets)
+		return -ENOMEM;
 	i = 0;
 	/* Walk through entries, checking offsets. */
 	xt_entry_foreach(iter, entry0, newinfo->size) {
···
 						 repl->underflow,
 						 repl->valid_hooks);
 		if (ret != 0)
-			return ret;
+			goto out_free;
+		if (i < repl->num_entries)
+			offsets[i] = (void *)iter - entry0;
 		++i;
 		if (strcmp(ip6t_get_target(iter)->u.user.name,
 		    XT_ERROR_TARGET) == 0)
 			++newinfo->stacksize;
 	}
 
+	ret = -EINVAL;
 	if (i != repl->num_entries)
-		return -EINVAL;
+		goto out_free;
 
 	/* Check hooks all assigned */
 	for (i = 0; i < NF_INET_NUMHOOKS; i++) {
···
 		if (!(repl->valid_hooks & (1 << i)))
 			continue;
 		if (newinfo->hook_entry[i] == 0xFFFFFFFF)
-			return -EINVAL;
+			goto out_free;
 		if (newinfo->underflow[i] == 0xFFFFFFFF)
-			return -EINVAL;
+			goto out_free;
 	}
 
-	if (!mark_source_chains(newinfo, repl->valid_hooks, entry0))
-		return -ELOOP;
+	if (!mark_source_chains(newinfo, repl->valid_hooks, entry0, offsets)) {
+		ret = -ELOOP;
+		goto out_free;
+	}
+	kvfree(offsets);
 
 	/* Finally, each sanity check must pass */
 	i = 0;
···
 		return ret;
 	}
 
+	return ret;
+ out_free:
+	kvfree(offsets);
 	return ret;
 }
 

net/netfilter/x_tables.c

···
 }
 EXPORT_SYMBOL(xt_check_entry_offsets);
 
+/**
+ * xt_alloc_entry_offsets - allocate array to store rule head offsets
+ *
+ * @size: number of entries
+ *
+ * Return: NULL or kmalloc'd or vmalloc'd array
+ */
+unsigned int *xt_alloc_entry_offsets(unsigned int size)
+{
+	unsigned int *off;
+
+	off = kcalloc(size, sizeof(unsigned int), GFP_KERNEL | __GFP_NOWARN);
+
+	if (off)
+		return off;
+
+	if (size < (SIZE_MAX / sizeof(unsigned int)))
+		off = vmalloc(size * sizeof(unsigned int));
+
+	return off;
+}
+EXPORT_SYMBOL(xt_alloc_entry_offsets);
+
+/**
+ * xt_find_jump_offset - check if target is a valid jump offset
+ *
+ * @offsets: array containing all valid rule start offsets of a rule blob
+ * @target: the jump target to search for
+ * @size: entries in @offset
+ */
+bool xt_find_jump_offset(const unsigned int *offsets,
+			 unsigned int target, unsigned int size)
+{
+	int m, low = 0, hi = size;
+
+	while (hi > low) {
+		m = (low + hi) / 2u;
+
+		if (offsets[m] > target)
+			hi = m;
+		else if (offsets[m] < target)
+			low = m + 1;
+		else
+			return true;
+	}
+
+	return false;
+}
+EXPORT_SYMBOL(xt_find_jump_offset);
+
 int xt_check_target(struct xt_tgchk_param *par,
 		    unsigned int size, u_int8_t proto, bool inv_proto)
 {