[PATCH 5.4 68/90] xfrm interface: fix packet tx through bpf_redirect()

Greg Kroah-Hartman
2020-02-03T16:36:26Z

From: Nicolas Dichtel <nicolas.dichtel@6wind.com>

[ Upstream commit f042365dbffea98fb8148c98c700402e8d099f02 ]

With an ebpf program that redirects packets through a xfrm interface,
packets are dropped because no dst is attached to skb.

This could also be reproduced with an AF_PACKET socket, with the following
python script (xfrm1 is a xfrm interface):

import socket
send_s = socket.socket(socket.AF_PACKET, socket.SOCK_RAW, 0)
# scapy
# p = IP(src='10.100.0.2', dst='10.200.0.1')/ICMP(type='echo-request')
# raw(p)
req = b'E\x00\x00\x1c\x00\x01\x00\x00@\x01e\xb2\nd\x00\x02\n\xc8\x00\x01\x08\x00\xf7\xff\x00\x00\x00\x00'
send_s.sendto(req, ('xfrm1', 0x800, 0, 0))

It was also not possible to send an ip packet through an AF_PACKET socket
because a LL header was expected. Let's remove those LL header constraints.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/xfrm/xfrm_interface.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index 0f5131bc3342d..a3db19d93fc5b 100644
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -268,9 +268,6 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
int err = -1;
int mtu;

- if (!dst)
- goto tx_err_link_failure;
-
dst_hold(dst);
dst = xfrm_lookup_with_ifid(xi->net, dst, fl, NULL, 0, xi->p.if_id);
if (IS_ERR(dst)) {
@@ -343,6 +340,7 @@ static netdev_tx_t xfrmi_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct xfrm_if *xi = netdev_priv(dev);
struct net_device_stats *stats = &xi->dev->stats;
+ struct dst_entry *dst = skb_dst(skb);
struct flowi fl;
int ret;

@@ -352,10 +350,33 @@ static netdev_tx_t xfrmi_xmit(struct sk_buff *skb, struct net_device *dev)
case htons(ETH_P_IPV6):
xfrm_decode_session(skb, &fl, AF_INET6);
memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
+ if (!dst) {
+ fl.u.ip6.flowi6_oif = dev->ifindex;
+ fl.u.ip6.flowi6_flags |= FLOWI_FLAG_ANYSRC;
+ dst = ip6_route_output(dev_net(dev), NULL, &fl.u.ip6);
+ if (dst->error) {
+ dst_release(dst);
+ stats->tx_carrier_errors++;
+ goto tx_err;
+ }
+ skb_dst_set(skb, dst);
+ }
break;
case htons(ETH_P_IP):
xfrm_decode_session(skb, &fl, AF_INET);
memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
+ if (!dst) {
+ struct rtable *rt;
+
+ fl.u.ip4.flowi4_oif = dev->ifindex;
+ fl.u.ip4.flowi4_flags |= FLOWI_FLAG_ANYSRC;
+ rt = __ip_route_output_key(dev_net(dev), &fl.u.ip4);
+ if (IS_ERR(rt)) {
+ stats->tx_carrier_errors++;
+ goto tx_err;
+ }
+ skb_dst_set(skb, &rt->dst);
+ }
break;
default:
goto tx_err;
@@ -563,12 +584,9 @@ static void xfrmi_dev_setup(struct net_device *dev)
{
dev->netdev_ops = &xfrmi_netdev_ops;
dev->type = ARPHRD_NONE;
- dev->hard_header_len = ETH_HLEN;
- dev->min_header_len = ETH_HLEN;
dev->mtu = ETH_DATA_LEN;
dev->min_mtu = ETH_MIN_MTU;
- dev->max_mtu = ETH_DATA_LEN;
- dev->addr_len = ETH_ALEN;
+ dev->max_mtu = IP_MAX_MTU;
dev->flags = IFF_NOARP;
dev->needs_free_netdev = true;
dev->priv_destructor = xfrmi_dev_free;
--
2.20.1