From: Lahav Schlesinger lschlesinger@drivenets.com
[ Upstream commit 09e856d54bda5f288ef8437a90ab2b9b3eab83d1 ]
To fix the "reverse-NAT" for replies.
When a packet is sent over a VRF, the POST_ROUTING hooks are called twice: Once from the VRF interface, and once from the "actual" interface the packet will be sent from: 1) First SNAT: l3mdev_l3_out() -> vrf_l3_out() -> .. -> vrf_output_direct() This causes the POST_ROUTING hooks to run. 2) Second SNAT: 'ip_output()' calls POST_ROUTING hooks again.
Similarly for replies, first ip_rcv() calls PRE_ROUTING hooks, and second vrf_l3_rcv() calls them again.
As an example, consider the following SNAT rule:
iptables -t nat -A POSTROUTING -p udp -m udp --dport 53 -j SNAT --to-source 2.2.2.2 -o vrf_1
In this case sending over a VRF will create 2 conntrack entries. The first is from the VRF interface, which performs the IP SNAT. The second will run the SNAT, but since the "expected reply" will remain the same, conntrack randomizes the source port of the packet: e..g With a socket bound to 1.1.1.1:10000, sending to 3.3.3.3:53, the conntrack rules are: udp 17 29 src=2.2.2.2 dst=3.3.3.3 sport=10000 dport=53 packets=1 bytes=68 [UNREPLIED] src=3.3.3.3 dst=2.2.2.2 sport=53 dport=61033 packets=0 bytes=0 mark=0 use=1 udp 17 29 src=1.1.1.1 dst=3.3.3.3 sport=10000 dport=53 packets=1 bytes=68 [UNREPLIED] src=3.3.3.3 dst=2.2.2.2 sport=53 dport=10000 packets=0 bytes=0 mark=0 use=1
i.e. First SNAT IP from 1.1.1.1 --> 2.2.2.2, and second the src port is SNAT-ed from 10000 --> 61033.
But when a reply is sent (3.3.3.3:53 -> 2.2.2.2:61033) only the later conntrack entry is matched: udp 17 29 src=2.2.2.2 dst=3.3.3.3 sport=10000 dport=53 packets=1 bytes=68 src=3.3.3.3 dst=2.2.2.2 sport=53 dport=61033 packets=1 bytes=49 mark=0 use=1 udp 17 28 src=1.1.1.1 dst=3.3.3.3 sport=10000 dport=53 packets=1 bytes=68 [UNREPLIED] src=3.3.3.3 dst=2.2.2.2 sport=53 dport=10000 packets=0 bytes=0 mark=0 use=1
And a "port 61033 unreachable" ICMP packet is sent back.
The issue is that when PRE_ROUTING hooks are called from vrf_l3_rcv(), the skb already has a conntrack flow attached to it, which means nf_conntrack_in() will not resolve the flow again.
This means only the dest port is "reverse-NATed" (61033 -> 10000) but the dest IP remains 2.2.2.2, and since the socket is bound to 1.1.1.1 it's not received. This can be verified by logging the 4-tuple of the packet in '__udp4_lib_rcv()'.
The fix is then to reset the flow when skb is received on a VRF, to let conntrack resolve the flow again (which now will hit the earlier flow).
To reproduce: (Without the fix "Got pkt_to_nat_port" will not be printed by running 'bash ./repro'): $ cat run_in_A1.py import logging logging.getLogger("scapy.runtime").setLevel(logging.ERROR) from scapy.all import * import argparse
def get_packet_to_send(udp_dst_port, msg_name): return Ether(src='11:22:33:44:55:66', dst=iface_mac)/ \ IP(src='3.3.3.3', dst='2.2.2.2')/ \ UDP(sport=53, dport=udp_dst_port)/ \ Raw(f'{msg_name}\x0012345678901234567890')
parser = argparse.ArgumentParser() parser.add_argument('-iface_mac', dest="iface_mac", type=str, required=True, help="From run_in_A3.py") parser.add_argument('-socket_port', dest="socket_port", type=str, required=True, help="From run_in_A3.py") parser.add_argument('-v1_mac', dest="v1_mac", type=str, required=True, help="From script")
args, _ = parser.parse_known_args() iface_mac = args.iface_mac socket_port = int(args.socket_port) v1_mac = args.v1_mac
print(f'Source port before NAT: {socket_port}')
while True: pkts = sniff(iface='_v0', store=True, count=1, timeout=10) if 0 == len(pkts): print('Something failed, rerun the script :(', flush=True) break pkt = pkts[0] if not pkt.haslayer('UDP'): continue
pkt_sport = pkt.getlayer('UDP').sport print(f'Source port after NAT: {pkt_sport}', flush=True)
pkt_to_send = get_packet_to_send(pkt_sport, 'pkt_to_nat_port') sendp(pkt_to_send, '_v0', verbose=False) # Will not be received
pkt_to_send = get_packet_to_send(socket_port, 'pkt_to_socket_port') sendp(pkt_to_send, '_v0', verbose=False) break
$ cat run_in_A2.py import socket import netifaces
print(f"{netifaces.ifaddresses('e00000')[netifaces.AF_LINK][0]['addr']}", flush=True) s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.setsockopt(socket.SOL_SOCKET, socket.SO_BINDTODEVICE, str('vrf_1' + '\0').encode('utf-8')) s.connect(('3.3.3.3', 53)) print(f'{s. getsockname()[1]}', flush=True) s.settimeout(5)
while True: try: # Periodically send in order to keep the conntrack entry alive. s.send(b'a'*40) resp = s.recvfrom(1024) msg_name = resp[0].decode('utf-8').split('\0')[0] print(f"Got {msg_name}", flush=True) except Exception as e: pass
$ cat repro.sh ip netns del A1 2> /dev/null ip netns del A2 2> /dev/null ip netns add A1 ip netns add A2
ip -n A1 link add _v0 type veth peer name _v1 netns A2 ip -n A1 link set _v0 up
ip -n A2 link add e00000 type bond ip -n A2 link add lo0 type dummy ip -n A2 link add vrf_1 type vrf table 10001 ip -n A2 link set vrf_1 up ip -n A2 link set e00000 master vrf_1
ip -n A2 addr add 1.1.1.1/24 dev e00000 ip -n A2 link set e00000 up ip -n A2 link set _v1 master e00000 ip -n A2 link set _v1 up ip -n A2 link set lo0 up ip -n A2 addr add 2.2.2.2/32 dev lo0
ip -n A2 neigh add 1.1.1.10 lladdr 77:77:77:77:77:77 dev e00000 ip -n A2 route add 3.3.3.3/32 via 1.1.1.10 dev e00000 table 10001
ip netns exec A2 iptables -t nat -A POSTROUTING -p udp -m udp --dport 53 -j \ SNAT --to-source 2.2.2.2 -o vrf_1
sleep 5 ip netns exec A2 python3 run_in_A2.py > x & XPID=$! sleep 5
IFACE_MAC=`sed -n 1p x` SOCKET_PORT=`sed -n 2p x` V1_MAC=`ip -n A2 link show _v1 | sed -n 2p | awk '{print $2'}` ip netns exec A1 python3 run_in_A1.py -iface_mac ${IFACE_MAC} -socket_port \ ${SOCKET_PORT} -v1_mac ${SOCKET_PORT} sleep 5
kill -9 $XPID wait $XPID 2> /dev/null ip netns del A1 ip netns del A2 tail x -n 2 rm x set +x
Fixes: 73e20b761acf ("net: vrf: Add support for PREROUTING rules on vrf device") Signed-off-by: Lahav Schlesinger lschlesinger@drivenets.com Reviewed-by: David Ahern dsahern@kernel.org Link: https://lore.kernel.org/r/20210815120002.2787653-1-lschlesinger@drivenets.co... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/vrf.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c index f08ed52d51f3..9b626c169554 100644 --- a/drivers/net/vrf.c +++ b/drivers/net/vrf.c @@ -1036,6 +1036,8 @@ static struct sk_buff *vrf_ip6_rcv(struct net_device *vrf_dev, bool need_strict = rt6_need_strict(&ipv6_hdr(skb)->daddr); bool is_ndisc = ipv6_ndisc_frame(skb);
+ nf_reset_ct(skb); + /* loopback, multicast & non-ND link-local traffic; do not push through * packet taps again. Reset pkt_type for upper layers to process skb. * For strict packets with a source LLA, determine the dst using the @@ -1092,6 +1094,8 @@ static struct sk_buff *vrf_ip_rcv(struct net_device *vrf_dev, skb->skb_iif = vrf_dev->ifindex; IPCB(skb)->flags |= IPSKB_L3SLAVE;
+ nf_reset_ct(skb); + if (ipv4_is_multicast(ip_hdr(skb)->daddr)) goto out;