4.9-stable review patch. If anyone has any objections, please let me know.
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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; }