netdev - [PATCH ipsec 2/2] xfrm interface: fix packet tx through bpf

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Message-Id: <20191231165654.19434-3-nicolas.dichtel@6wind.com>
Date:   Tue, 31 Dec 2019 17:56:54 +0100
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     steffen.klassert@...unet.com, davem@...emloft.net
Cc:     netdev@...r.kernel.org, Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: [PATCH ipsec 2/2] xfrm interface: fix packet tx through bpf_redirect()

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@...nd.com>
---
 net/xfrm/xfrm_interface.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index 7ac1542feaf8..55978a1501ec 100644
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -343,6 +343,7 @@ 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 +353,26 @@ 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) {
+			dst = ip6_route_output(dev_net(dev), NULL, &fl.u.ip6);
+			if (dst->error) {
+				dst_release(dst);
+				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 = __ip_route_output_key(dev_net(dev),
+								  &fl.u.ip4);
+
+			if (IS_ERR(rt))
+				goto tx_err;
+			skb_dst_set(skb, &rt->dst);
+		}
 		break;
 	default:
 		goto tx_err;
@@ -563,12 +580,9 @@ 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;
-- 
2.24.0