netfilter: add back stackpointer size checks

The rationale for removing the check is only correct for rulesets
generated by ip(6)tables.

In iptables, a jump can only occur to a user-defined chain, i.e.
because we size the stack based on number of user-defined chains we
cannot exceed stack size.

However, the underlying binary format has no such restriction,
and the validation step only ensures that the jump target is a
valid rule start point.

IOW, its possible to build a rule blob that has no user-defined
chains but does contain a jump.

If this happens, no jump stack gets allocated and crash occurs
because no jumpstack was allocated.

Fixes: 7814b6ec6d0d6 ("netfilter: xtables: don't save/restore jumpstack offset")
Reported-by: syzbot+e783f671527912cd9403@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 4ffe302..e3e420f 100644 (file)
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -252,6 +252,10 @@ unsigned int arpt_do_table(struct sk_buff *skb,
                        }
                        if (table_base + v
                            != arpt_next_entry(e)) {
+                               if (unlikely(stackidx >= private->stacksize)) {
+                                       verdict = NF_DROP;
+                                       break;
+                               }
                                jumpstack[stackidx++] = e;
                        }
 

diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 9a71f31..e38395a 100644 (file)
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -330,8 +330,13 @@ ipt_do_table(struct sk_buff *skb,
                                continue;
                        }
                        if (table_base + v != ipt_next_entry(e) &&
-                           !(e->ip.flags & IPT_F_GOTO))
+                           !(e->ip.flags & IPT_F_GOTO)) {
+                               if (unlikely(stackidx >= private->stacksize)) {
+                                       verdict = NF_DROP;
+                                       break;
+                               }
                                jumpstack[stackidx++] = e;
+                       }
 
                        e = get_entry(table_base, v);
                        continue;

diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index af4c917..62358b9 100644 (file)
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -352,6 +352,10 @@ ip6t_do_table(struct sk_buff *skb,
                        }
                        if (table_base + v != ip6t_next_entry(e) &&
                            !(e->ipv6.flags & IP6T_F_GOTO)) {
+                               if (unlikely(stackidx >= private->stacksize)) {
+                                       verdict = NF_DROP;
+                                       break;
+                               }
                                jumpstack[stackidx++] = e;
                        }