netfilter: x_tables: validate targets of jumps

Orabug: 24690280
CVE: CVE-2016-3134

[ Upstream commit 36472341017529e2b12573093cc0f68719300997 ]

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@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 8163327a3a927c36f7c032bb67957e6c0f4ec27d)
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 82ceed05f202d4a9240d46d971e2b5f4c0b3498f..538839daf110d2f0b290ef0b4c12344e485caa84 100644 (file)
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -362,6 +362,18 @@ static inline bool unconditional(const struct arpt_entry *e)
               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.
  */