netfilter: add back stackpointer size checks

commit 57ebd808a97d7c5b1e1afb937c2db22beba3c1f8 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 4cfcc22f7430d57cd6902a238a82a6b81f1f23ac..c18f0554b87cd3a735b392c62d99e117e39995fb 100644 (file)
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -329,6 +329,10 @@ 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 a98173d1ea97a73f8e31d4e29fc695f3500a09df..0bcf906bc4fb6d2a88deb880e0a264fc30c8bb5f 100644 (file)
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -408,6 +408,10 @@ ipt_do_table(struct sk_buff *skb,
                        }
                        if (table_base + v != ipt_next_entry(e) &&
                            !(e->ip.flags & IPT_F_GOTO)) {
+                               if (unlikely(stackidx >= private->stacksize)) {
+                                       verdict = NF_DROP;
+                                       break;
+                               }
                                jumpstack[stackidx++] = e;
                                pr_debug("Pushed %p into pos %u\n",
                                         e, stackidx - 1);

diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index bb1b5453a7a1ee7bf54b8763a4de6d54e18e9632..32d64e023b89293622c4163e00023d8521c0efd4 100644 (file)
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -425,6 +425,10 @@ 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;
                        }