[PATCH 4.9 54/86] netfilter: add back stackpointer size checks

Greg Kroah-Hartman
2018-03-16T15:23:17Z

From: Florian Westphal <fw@strlen.de>

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>

---
net/ipv4/netfilter/arp_tables.c | 4 ++++
net/ipv4/netfilter/ip_tables.c | 7 ++++++-
net/ipv6/netfilter/ip6_tables.c | 4 ++++
3 files changed, 14 insertions(+), 1 deletion(-)

--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -261,6 +261,10 @@ unsigned int arpt_do_table(struct sk_buf
}
if (table_base + v
!= arpt_next_entry(e)) {
+ if (unlikely(stackidx >= private->stacksize)) {
+ verdict = NF_DROP;
+ break;
+ }
jumpstack[stackidx++] = e;
}

--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -345,8 +345,13 @@ 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;
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -376,6 +376,10 @@ 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;
}