xfrm: move xfrm_garbage_collect out of xfrm_policy_flush

Now we will force to do garbage collection if any policy removed in
xfrm_policy_flush(). But during xfrm_net_exit(). We call flow_cache_fini()
first and set set fc->percpu to NULL. Then after we call xfrm_policy_fini()
-> frxm_policy_flush() -> flow_cache_flush(), we will get NULL pointer
dereference when check percpu_empty. The code path looks like:

flow_cache_fini()
  - fc->percpu = NULL
xfrm_policy_fini()
  - xfrm_policy_flush()
    - xfrm_garbage_collect()
      - flow_cache_flush()
        - flow_cache_percpu_empty()
	  - fcp = per_cpu_ptr(fc->percpu, cpu)

To reproduce, just add ipsec in netns and then remove the netns.

v2:
As Xin Long suggested, since only two other places need to call it. move
xfrm_garbage_collect() outside xfrm_policy_flush().

v3:
Fix subject mismatch after v2 fix.

Fixes: 35db06912189 ("xfrm: do the garbage collection after flushing policy")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 38614df33ec8..86116e9aaf3d 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2027,6 +2027,7 @@ static int xfrm_flush_policy(struct sk_buff *skb, struct nlmsghdr *nlh,
 			return 0;
 		return err;
 	}
+	xfrm_garbage_collect(net);
 
 	c.data.type = type;
 	c.event = nlh->nlmsg_type;