[PATCH] ipv4: icmp: use skb_dst_dev_net_rcu() in icmp_build_probe

[Haoran Wang <haoranwangsec@gmail.com>]

icmp_build_probe() derives the network namespace from the ingress device.

    /* net/ipv4/icmp.c:1296 */
    struct net *net = dev_net_rcu(skb->dev);

The ICMP Extended Echo (RFC 8335) PROBE replies identify the queried
interface by name/index/address and should look it up and apply policy
in the netns the packet is destined to, not the netns of the ingress
device.  Under a VRF, skb->dev is the VRF master, so dev_net_rcu(skb->dev)
returns the master's netns and the device lookup / reply policy run in
the wrong namespace.

The rest of the IPv4 ICMP echo path already uses skb_dst_dev_net_rcu(skb)
(net/ipv4/icmp.c:1123, :1267, :1437), while icmp_build_probe() is the
exception.


Signed-off-by: Haoran Wang <haoranwangsec@gmail.com>
---
 net/ipv4/icmp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 90c0e22c2..a577dfc65 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -1293,7 +1293,7 @@ static enum skb_drop_reason icmp_echo(struct sk_buff *skb)
 
 bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
 {
-	struct net *net = dev_net_rcu(skb->dev);
+	struct net *net = skb_dst_dev_net_rcu(skb);
 	struct icmp_ext_hdr *ext_hdr, _ext_hdr;
 	struct icmp_ext_echo_iio *iio, _iio;
 	struct inet6_dev *in6_dev;