From: Chieh-Min Wang chiehminw@synology.com
[ Upstream commit 13f5251fd17088170c18844534682d9cab5ff5aa ]
For bridge(br_flood) or broadcast/multicast packets, they could clone skb with unconfirmed conntrack which break the rule that unconfirmed skb->_nfct is never shared. With nfqueue running on my system, the race can be easily reproduced with following warning calltrace:
[13257.707525] CPU: 0 PID: 12132 Comm: main Tainted: P W 4.4.60 #7744 [13257.707568] Hardware name: Qualcomm (Flattened Device Tree) [13257.714700] [<c021f6dc>] (unwind_backtrace) from [<c021bce8>] (show_stack+0x10/0x14) [13257.720253] [<c021bce8>] (show_stack) from [<c0449e10>] (dump_stack+0x94/0xa8) [13257.728240] [<c0449e10>] (dump_stack) from [<c022a7e0>] (warn_slowpath_common+0x94/0xb0) [13257.735268] [<c022a7e0>] (warn_slowpath_common) from [<c022a898>] (warn_slowpath_null+0x1c/0x24) [13257.743519] [<c022a898>] (warn_slowpath_null) from [<c06ee450>] (__nf_conntrack_confirm+0xa8/0x618) [13257.752284] [<c06ee450>] (__nf_conntrack_confirm) from [<c0772670>] (ipv4_confirm+0xb8/0xfc) [13257.761049] [<c0772670>] (ipv4_confirm) from [<c06e7a60>] (nf_iterate+0x48/0xa8) [13257.769725] [<c06e7a60>] (nf_iterate) from [<c06e7af0>] (nf_hook_slow+0x30/0xb0) [13257.777108] [<c06e7af0>] (nf_hook_slow) from [<c07f20b4>] (br_nf_post_routing+0x274/0x31c) [13257.784486] [<c07f20b4>] (br_nf_post_routing) from [<c06e7a60>] (nf_iterate+0x48/0xa8) [13257.792556] [<c06e7a60>] (nf_iterate) from [<c06e7af0>] (nf_hook_slow+0x30/0xb0) [13257.800458] [<c06e7af0>] (nf_hook_slow) from [<c07e5580>] (br_forward_finish+0x94/0xa4) [13257.808010] [<c07e5580>] (br_forward_finish) from [<c07f22ac>] (br_nf_forward_finish+0x150/0x1ac) [13257.815736] [<c07f22ac>] (br_nf_forward_finish) from [<c06e8df0>] (nf_reinject+0x108/0x170) [13257.824762] [<c06e8df0>] (nf_reinject) from [<c06ea854>] (nfqnl_recv_verdict+0x3d8/0x420) [13257.832924] [<c06ea854>] (nfqnl_recv_verdict) from [<c06e940c>] (nfnetlink_rcv_msg+0x158/0x248) [13257.841256] [<c06e940c>] (nfnetlink_rcv_msg) from [<c06e5564>] (netlink_rcv_skb+0x54/0xb0) [13257.849762] [<c06e5564>] (netlink_rcv_skb) from [<c06e4ec8>] (netlink_unicast+0x148/0x23c) [13257.858093] [<c06e4ec8>] (netlink_unicast) from [<c06e5364>] (netlink_sendmsg+0x2ec/0x368) [13257.866348] [<c06e5364>] (netlink_sendmsg) from [<c069fb8c>] (sock_sendmsg+0x34/0x44) [13257.874590] [<c069fb8c>] (sock_sendmsg) from [<c06a03dc>] (___sys_sendmsg+0x1ec/0x200) [13257.882489] [<c06a03dc>] (___sys_sendmsg) from [<c06a11c8>] (__sys_sendmsg+0x3c/0x64) [13257.890300] [<c06a11c8>] (__sys_sendmsg) from [<c0209b40>] (ret_fast_syscall+0x0/0x34)
The original code just triggered the warning but do nothing. It will caused the shared conntrack moves to the dying list and the packet be droppped (nf_ct_resolve_clash returns NF_DROP for dying conntrack).
- Reproduce steps:
+----------------------------+ | br0(bridge) | | | +-+---------+---------+------+ | eth0| | eth1| | eth2| | | | | | | +--+--+ +--+--+ +---+-+ | | | | | | +--+-+ +-+--+ +--+-+ | PC1| | PC2| | PC3| +----+ +----+ +----+
iptables -A FORWARD -m mark --mark 0x1000000/0x1000000 -j NFQUEUE --queue-num 100 --queue-bypass
ps: Our nfq userspace program will set mark on packets whose connection has already been processed.
PC1 sends broadcast packets simulated by hping3:
hping3 --rand-source --udp 192.168.1.255 -i u100
- Broadcast racing flow chart is as follow:
br_handle_frame BR_HOOK(NFPROTO_BRIDGE, NF_BR_PRE_ROUTING, br_handle_frame_finish) // skb->_nfct (unconfirmed conntrack) is constructed at PRE_ROUTING stage br_handle_frame_finish // check if this packet is broadcast br_flood_forward br_flood list_for_each_entry_rcu(p, &br->port_list, list) // iterate through each port maybe_deliver deliver_clone skb = skb_clone(skb) __br_forward BR_HOOK(NFPROTO_BRIDGE, NF_BR_FORWARD,...) // queue in our nfq and received by our userspace program // goto __nf_conntrack_confirm with process context on CPU 1 br_pass_frame_up BR_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN,...) // goto __nf_conntrack_confirm with softirq context on CPU 0
Because conntrack confirm can happen at both INPUT and POSTROUTING stage. So with NFQUEUE running, skb->_nfct with the same unconfirmed conntrack could race on different core.
This patch fixes a repeating kernel splat, now it is only displayed once.
Signed-off-by: Chieh-Min Wang chiehminw@synology.com Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/netfilter/nf_conntrack_core.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 895171a2e1f1..9a249478abf2 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -901,10 +901,18 @@ __nf_conntrack_confirm(struct sk_buff *skb) * REJECT will give spurious warnings here. */
- /* No external references means no one else could have - * confirmed us. + /* Another skb with the same unconfirmed conntrack may + * win the race. This may happen for bridge(br_flood) + * or broadcast/multicast packets do skb_clone with + * unconfirmed conntrack. */ - WARN_ON(nf_ct_is_confirmed(ct)); + if (unlikely(nf_ct_is_confirmed(ct))) { + WARN_ON_ONCE(1); + nf_conntrack_double_unlock(hash, reply_hash); + local_bh_enable(); + return NF_DROP; + } + pr_debug("Confirming conntrack %p\n", ct); /* We have to check the DYING flag after unlink to prevent * a race against nf_ct_get_next_corpse() possibly called from