From 57ebd808a97d7c5b1e1afb937c2db22beba3c1f8 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Wed, 7 Feb 2018 13:46:25 +0100 Subject: 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 Signed-off-by: Pablo Neira Ayuso --- net/ipv6/netfilter/ip6_tables.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'net/ipv6') diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c index af4c917e0836..62358b93bbac 100644 --- 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; } -- cgit v1.2.3-59-g8ed1b