[PATCH net-next 2/7] xfrm: Switch to skb_dst_reset to clear dst_entry

[Stanislav Fomichev <sdf@fomichev.me>]

Going forward skb_dst_set will assert that skb dst_entry
is empty during skb_dst_set. skb_dst_reset is added to reset
existing entry without doing refcnt. Switch to skb_dst_reset
in __xfrm_route_forward and add a comment on why it's safe
to skip skb_dst_restore.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
---
 net/xfrm/xfrm_policy.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index c5035a9bc3bb..a5ffe26b64d5 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3881,12 +3881,18 @@ int __xfrm_route_forward(struct sk_buff *skb, unsigned short family)
 	}
 
 	skb_dst_force(skb);
-	if (!skb_dst(skb)) {
+	dst = skb_dst(skb);
+	if (!dst) {
 		XFRM_INC_STATS(net, LINUX_MIB_XFRMFWDHDRERROR);
 		return 0;
 	}
 
-	dst = xfrm_lookup(net, skb_dst(skb), &fl, NULL, XFRM_LOOKUP_QUEUE);
+	/* ignore return value from skb_dst_reset, xfrm_lookup takes
+	 * care of dropping the refcnt if needed.
+	 */
+	skb_dst_reset(skb);
+
+	dst = xfrm_lookup(net, dst, &fl, NULL, XFRM_LOOKUP_QUEUE);
 	if (IS_ERR(dst)) {
 		res = 0;
 		dst = NULL;
-- 
2.50.1