The issue happens on an error path in __xfrm_policy_check(). When the
fetching process of the object `pols[1]` fails, the function simply
returns 0, forgetting to decrement the reference count of `pols[0]`,
which is incremented earlier by either xfrm_sk_policy_lookup() or
xfrm_policy_lookup(). This may result in memory leaks.

Fix it by decreasing the reference count of `pols[0]` in that path.

Fixes: 134b0fc5 ("IPsec: propagate security module errors up from flow_cache_lookup")
Signed-off-by: NXin Xiong <xiongx18@fudan.edu.cn>
Signed-off-by: NXin Tan <tanxin.ctf@gmail.com>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>