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[PATCH AUTOSEL 4.20 20/60] xfrm: Fix inbound traffic via XFRM interfaces across network namespaces

From: Tobias Brunner <tobias@xxxxxxxxxxxxxx>

[ Upstream commit 660899ddf06ae8bb5bbbd0a19418b739375430c5 ]

After moving an XFRM interface to another namespace it stays associated
with the original namespace (net in `struct xfrm_if` and the list keyed
with `xfrmi_net_id`), allowing processes in the new namespace to use
SAs/policies that were created in the original namespace.  For instance,
this allows a keying daemon in one namespace to establish IPsec SAs for
other namespaces without processes there having access to the keys or IKE

This worked fine for outbound traffic, however, for inbound traffic the
lookup for the interfaces and the policies used the incorrect namespace
(the one the XFRM interface was moved to).

Fixes: f203b76d7809 ("xfrm: Add virtual xfrm interfaces")
Signed-off-by: Tobias Brunner <tobias@xxxxxxxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
 net/xfrm/xfrm_interface.c | 4 ++--
 net/xfrm/xfrm_policy.c    | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index d679fa0f44b3..fcf3c714f4ff 100644
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -76,10 +76,10 @@ static struct xfrm_if *xfrmi_decode_session(struct sk_buff *skb)
 	int ifindex;
 	struct xfrm_if *xi;
-	if (!skb->dev)
+	if (!secpath_exists(skb) || !skb->dev)
 		return NULL;
-	xfrmn = net_generic(dev_net(skb->dev), xfrmi_net_id);
+	xfrmn = net_generic(xs_net(xfrm_input_state(skb)), xfrmi_net_id);
 	ifindex = skb->dev->ifindex;
 	for_each_xfrmi_rcu(xfrmn->xfrmi[0], xi) {
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 6ea8036fcdbe..bf5d59270f79 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2340,8 +2340,10 @@ int __xfrm_policy_check(struct sock *sk, int dir, struct sk_buff *skb,
 	if (ifcb) {
 		xi = ifcb->decode_session(skb);
-		if (xi)
+		if (xi) {
 			if_id = xi->p.if_id;
+			net = xi->net;
+		}