netdev - [PATCHv2 ipsec] xfrm: set dst dev to blackhole_netdev instead of loopback

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Date:   Sun, 15 May 2022 21:37:27 -0400
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>
Cc:     davem@...emloft.net, kuba@...nel.org,
        Eric Dumazet <edumazet@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: [PATCHv2 ipsec] xfrm: set dst dev to blackhole_netdev instead of loopback_dev in ifdown

The global blackhole_netdev has replaced pernet loopback_dev to become the
one given to the object that holds an netdev when ifdown in many places of
ipv4 and ipv6 since commit 8d7017fd621d ("blackhole_netdev: use
blackhole_netdev to invalidate dst entries").

Especially after commit faab39f63c1f ("net: allow out-of-order netdev
unregistration"), it's no longer safe to use loopback_dev that may be
freed before other netdev.

This patch is to set dst dev to blackhole_netdev instead of loopback_dev
in ifdown.

v1->v2:
  - add Fixes tag as Eric suggested.

Fixes: faab39f63c1f ("net: allow out-of-order netdev unregistration")
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/xfrm/xfrm_policy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 00bd0ecff5a1..f1876ea61fdc 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3744,7 +3744,7 @@ static int stale_bundle(struct dst_entry *dst)
 void xfrm_dst_ifdown(struct dst_entry *dst, struct net_device *dev)
 {
 	while ((dst = xfrm_dst_child(dst)) && dst->xfrm && dst->dev == dev) {
-		dst->dev = dev_net(dev)->loopback_dev;
+		dst->dev = blackhole_netdev;
 		dev_hold(dst->dev);
 		dev_put(dev);
 	}
-- 
2.31.1