[PATCH 07/21] netfilter: x_tables: validate targets of jumps

[Luis Henriques]

From: Florian Westphal <fw at strlen.de>

When we see a jump also check that the offset gets us to beginning of
a rule (an ipt_entry).

The extra overhead is negible, even with absurd cases.

300k custom rules, 300k jumps to 'next' user chain:
[ plus one jump from INPUT to first userchain ]:

Before:
real    0m24.874s
user    0m7.532s
sys     0m16.076s

After:
real    0m27.464s
user    0m7.436s
sys     0m18.840s

Signed-off-by: Florian Westphal <fw at strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo at netfilter.org>
(backported from commit 36472341017529e2b12573093cc0f68719300997)
[ luis: based on Florian's backport to 3.14:
   "Need to pass the start of the ruleset as extra argument as
    t->entries won't work in 3.14 (its percpu and not even set
    up for all processors at this point)." ]
BugLink: https://bugs.launchpad.net/bugs/1595350
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ipv4/netfilter/arp_tables.c | 17 +++++++++++++++++
 net/ipv4/netfilter/ip_tables.c  | 17 +++++++++++++++++
 net/ipv6/netfilter/ip6_tables.c | 17 +++++++++++++++++
 3 files changed, 51 insertions(+)

diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index fa6a4387ffc2..0c31fa22fab3 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -374,6 +374,19 @@ static bool next_offset_ok(const struct xt_table_info *t, unsigned int newpos)
 	return true;
 }
 
+static bool find_jump_target(const struct xt_table_info *t,
+			     const void *entry0,
+			     const struct arpt_entry *target)
+{
+	struct arpt_entry *iter;
+
+	xt_entry_foreach(iter, entry0, 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.
  */
@@ -461,6 +474,10 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
 					/* This a jump; chase it. */
 					duprintf("Jump rule %u -> %u\n",
 						 pos, newpos);
+					e = (struct arpt_entry *)
+						(entry0 + newpos);
+					if (!find_jump_target(newinfo, entry0, e))
+						return 0;
 				} else {
 					/* ... this is a fallthru */
 					newpos = pos + e->next_offset;
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 797f45cf3572..9bfccbc627e7 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -450,6 +450,19 @@ static bool next_offset_ok(const struct xt_table_info *t, unsigned int newpos)
 	return true;
 }
 
+static bool find_jump_target(const struct xt_table_info *t,
+			     const void *entry0,
+			     const struct ipt_entry *target)
+{
+	struct ipt_entry *iter;
+
+	xt_entry_foreach(iter, entry0, 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
@@ -542,6 +555,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
 					/* This a jump; chase it. */
 					duprintf("Jump rule %u -> %u\n",
 						 pos, newpos);
+					e = (struct ipt_entry *)
+						(entry0 + newpos);
+					if (!find_jump_target(newinfo, entry0, e))
+						return 0;
 				} else {
 					/* ... this is a fallthru */
 					newpos = pos + e->next_offset;
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index ab87032cd113..c1bc98c7cbf0 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -460,6 +460,19 @@ static bool next_offset_ok(const struct xt_table_info *t, unsigned int newpos)
 	return true;
 }
 
+static bool find_jump_target(const struct xt_table_info *t,
+			     const void *entry0,
+			     const struct ip6t_entry *target)
+{
+	struct ip6t_entry *iter;
+
+	xt_entry_foreach(iter, entry0, 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
@@ -552,6 +565,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
 					/* This a jump; chase it. */
 					duprintf("Jump rule %u -> %u\n",
 						 pos, newpos);
+					e = (struct ip6t_entry *)
+						(entry0 + newpos);
+					if (!find_jump_target(newinfo, entry0, e))
+						return 0;
 				} else {
 					/* ... this is a fallthru */
 					newpos = pos + e->next_offset;