[PATCH 3/8] xfrm: Wait for RCU readers during policy netns exit

[Steffen Klassert <steffen.klassert@secunet.com>]

xfrm_policy_fini() frees the policy_bydst hash tables after flushing the
policy work items and deleting all policies, but it does not wait for
concurrent RCU readers to leave their read-side critical sections first.

The policy_bydst tables are published via rcu_assign_pointer() and are
looked up through rcu_dereference_check(), so netns teardown must also
wait for an RCU grace period before freeing the table memory.

Fix this by adding synchronize_rcu() before freeing the policy hash tables.

Fixes: e1e551bc5630 ("xfrm: policy: prepare policy_bydst hash for rcu lookups")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
---
 net/xfrm/xfrm_policy.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 362939aa56cf..8f0188e763c7 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -4290,6 +4290,8 @@ static void xfrm_policy_fini(struct net *net)
 #endif
 	xfrm_policy_flush(net, XFRM_POLICY_TYPE_MAIN, false);
 
+	synchronize_rcu();
+
 	WARN_ON(!list_empty(&net->xfrm.policy_all));
 
 	for (dir = 0; dir < XFRM_POLICY_MAX; dir++) {
-- 
2.43.0