| Message ID | 20170727022204.17843-1-ap420073@gmail.com |
|---|---|
| State | Accepted |
| Delegated to: | Pablo Neira |
| Headers | show |
On Thu, Jul 27, 2017 at 11:22:04AM +0900, Taehee Yoo wrote: > If verdict is NF_STOLEN in the SYNPROXY target, > the skb is consumed. > However, ipt_do_table() always tries to get ip header from the skb. > So that, KASAN triggers the use-after-free message. > > We can reproduce this message using below command. > # iptables -I INPUT -p tcp -j SYNPROXY --mss 1460 > > [ 193.542265] BUG: KASAN: use-after-free in ipt_do_table+0x1405/0x1c10 > [ ... ] > [ 193.578603] Call Trace: > [ 193.581590] <IRQ> > [ 193.584107] dump_stack+0x68/0xa0 > [ 193.588168] print_address_description+0x78/0x290 > [ 193.593828] ? ipt_do_table+0x1405/0x1c10 > [ 193.598690] kasan_report+0x230/0x340 > [ 193.603194] __asan_report_load2_noabort+0x19/0x20 > [ 193.608950] ipt_do_table+0x1405/0x1c10 > [ 193.613591] ? rcu_read_lock_held+0xae/0xd0 > [ 193.618631] ? ip_route_input_rcu+0x27d7/0x4270 > [ 193.624348] ? ipt_do_table+0xb68/0x1c10 > [ 193.629124] ? do_add_counters+0x620/0x620 > [ 193.634234] ? iptable_filter_net_init+0x60/0x60 > [ ... ] > > After this patch, only when verdict is XT_CONTINUE, > ipt_do_table() tries to get ip header. > Also arpt_do_table() is modified because it has same bug. Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c index 0bc3c3d..9e9d9af 100644 --- a/net/ipv4/netfilter/arp_tables.c +++ b/net/ipv4/netfilter/arp_tables.c @@ -268,14 +268,14 @@ unsigned int arpt_do_table(struct sk_buff *skb, acpar.targinfo = t->data; verdict = t->u.kernel.target->target(skb, &acpar); - /* Target might have changed stuff. */ - arp = arp_hdr(skb); - - if (verdict == XT_CONTINUE) + if (verdict == XT_CONTINUE) { + /* Target might have changed stuff. */ + arp = arp_hdr(skb); e = arpt_next_entry(e); - else + } else { /* Verdict */ break; + } } while (!acpar.hotdrop); xt_write_recseq_end(addend); local_bh_enable(); diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c index 2a55a40..622ed28 100644 --- a/net/ipv4/netfilter/ip_tables.c +++ b/net/ipv4/netfilter/ip_tables.c @@ -352,13 +352,14 @@ ipt_do_table(struct sk_buff *skb, acpar.targinfo = t->data; verdict = t->u.kernel.target->target(skb, &acpar); - /* Target might have changed stuff. */ - ip = ip_hdr(skb); - if (verdict == XT_CONTINUE) + if (verdict == XT_CONTINUE) { + /* Target might have changed stuff. */ + ip = ip_hdr(skb); e = ipt_next_entry(e); - else + } else { /* Verdict */ break; + } } while (!acpar.hotdrop); xt_write_recseq_end(addend);
If verdict is NF_STOLEN in the SYNPROXY target, the skb is consumed. However, ipt_do_table() always tries to get ip header from the skb. So that, KASAN triggers the use-after-free message. We can reproduce this message using below command. # iptables -I INPUT -p tcp -j SYNPROXY --mss 1460 [ 193.542265] BUG: KASAN: use-after-free in ipt_do_table+0x1405/0x1c10 [ ... ] [ 193.578603] Call Trace: [ 193.581590] <IRQ> [ 193.584107] dump_stack+0x68/0xa0 [ 193.588168] print_address_description+0x78/0x290 [ 193.593828] ? ipt_do_table+0x1405/0x1c10 [ 193.598690] kasan_report+0x230/0x340 [ 193.603194] __asan_report_load2_noabort+0x19/0x20 [ 193.608950] ipt_do_table+0x1405/0x1c10 [ 193.613591] ? rcu_read_lock_held+0xae/0xd0 [ 193.618631] ? ip_route_input_rcu+0x27d7/0x4270 [ 193.624348] ? ipt_do_table+0xb68/0x1c10 [ 193.629124] ? do_add_counters+0x620/0x620 [ 193.634234] ? iptable_filter_net_init+0x60/0x60 [ ... ] After this patch, only when verdict is XT_CONTINUE, ipt_do_table() tries to get ip header. Also arpt_do_table() is modified because it has same bug. Signed-off-by: Taehee Yoo <ap420073@gmail.com> --- V3: - Modified arpt_do_table() is added. V2: - Change commit log message. V1: - Initial Version net/ipv4/netfilter/arp_tables.c | 10 +++++----- net/ipv4/netfilter/ip_tables.c | 9 +++++---- 2 files changed, 10 insertions(+), 9 deletions(-)