From: Vlad Buslov <vladbu@mellanox.com>
Date: Fri, 10 Aug 2018 20:51:44 +0300
Subject: net: sched: act_ife: remove dependency on rtnl lock
Patch-mainline: v4.19-rc1
Git-commit: 54d0d423a48aa0e61bb39665d20376ba7b940535
References: bsc#1109837

Use tcf spinlock and rcu to protect params pointer from concurrent
modification during dump and init. Use rcu swap operation to reassign
params pointer under protection of tcf lock. (old params value is not used
by init, so there is no need of standalone rcu dereference step)

Ife action has meta-actions that are compiled as standalone modules. Rtnl
mutex must be released while loading a kernel module. In order to support
execution without rtnl mutex, propagate 'rtnl_held' argument to meta action
loading functions. When requesting meta action module, conditionally
release rtnl lock depending on 'rtnl_held' argument.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/sched/act_ife.c |   40 +++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 15 deletions(-)

--- a/net/sched/act_ife.c
+++ b/net/sched/act_ife.c
@@ -268,7 +268,8 @@ static const char *ife_meta_id2name(u32
  * under ife->tcf_lock for existing action
 */
 static int load_metaops_and_vet(struct tcf_ife_info *ife, u32 metaid,
-				void *val, int len, bool exists)
+				void *val, int len, bool exists,
+				bool rtnl_held)
 {
 	struct tcf_meta_ops *ops = find_ife_oplist(metaid);
 	int ret = 0;
@@ -278,9 +279,11 @@ static int load_metaops_and_vet(struct t
 #ifdef CONFIG_MODULES
 		if (exists)
 			spin_unlock_bh(&ife->tcf_lock);
-		rtnl_unlock();
+		if (rtnl_held)
+			rtnl_unlock();
 		request_module("ife-meta-%s", ife_meta_id2name(metaid));
-		rtnl_lock();
+		if (rtnl_held)
+			rtnl_lock();
 		if (exists)
 			spin_lock_bh(&ife->tcf_lock);
 		ops = find_ife_oplist(metaid);
@@ -421,7 +424,7 @@ static void tcf_ife_cleanup(struct tc_ac
 
 /* under ife->tcf_lock for existing action */
 static int populate_metalist(struct tcf_ife_info *ife, struct nlattr **tb,
-			     bool exists)
+			     bool exists, bool rtnl_held)
 {
 	int len = 0;
 	int rc = 0;
@@ -433,7 +436,8 @@ static int populate_metalist(struct tcf_
 			val = nla_data(tb[i]);
 			len = nla_len(tb[i]);
 
-			rc = load_metaops_and_vet(ife, i, val, len, exists);
+			rc = load_metaops_and_vet(ife, i, val, len, exists,
+						  rtnl_held);
 			if (rc != 0)
 				return rc;
 
@@ -454,7 +458,7 @@ static int tcf_ife_init(struct net *net,
 	struct tc_action_net *tn = net_generic(net, ife_net_id);
 	struct nlattr *tb[TCA_IFE_MAX + 1];
 	struct nlattr *tb2[IFE_META_MAX + 1];
-	struct tcf_ife_params *p, *p_old;
+	struct tcf_ife_params *p;
 	struct tcf_ife_info *ife;
 	u16 ife_type = ETH_P_IFE;
 	struct tc_ife *parm;
@@ -558,7 +562,7 @@ metadata_parse_err:
 			return err;
 		}
 
-		err = populate_metalist(ife, tb2, exists);
+		err = populate_metalist(ife, tb2, exists, rtnl_held);
 		if (err)
 			goto metadata_parse_err;
 
@@ -581,13 +585,13 @@ metadata_parse_err:
 	}
 
 	ife->tcf_action = parm->action;
+	/* protected by tcf_lock when modifying existing action */
+	rcu_swap_protected(ife->params, p, 1);
+
 	if (exists)
 		spin_unlock_bh(&ife->tcf_lock);
-
-	p_old = rtnl_dereference(ife->params);
-	rcu_assign_pointer(ife->params, p);
-	if (p_old)
-		kfree_rcu(p_old, rcu);
+	if (p)
+		kfree_rcu(p, rcu);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
@@ -600,16 +604,20 @@ static int tcf_ife_dump(struct sk_buff *
 {
 	unsigned char *b = skb_tail_pointer(skb);
 	struct tcf_ife_info *ife = to_ife(a);
-	struct tcf_ife_params *p = rtnl_dereference(ife->params);
+	struct tcf_ife_params *p;
 	struct tc_ife opt = {
 		.index = ife->tcf_index,
 		.refcnt = refcount_read(&ife->tcf_refcnt) - ref,
 		.bindcnt = atomic_read(&ife->tcf_bindcnt) - bind,
-		.action = ife->tcf_action,
-		.flags = p->flags,
 	};
 	struct tcf_t t;
 
+	spin_lock_bh(&ife->tcf_lock);
+	opt.action = ife->tcf_action;
+	p = rcu_dereference_protected(ife->params,
+				      lockdep_is_held(&ife->tcf_lock));
+	opt.flags = p->flags;
+
 	if (nla_put(skb, TCA_IFE_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
 
@@ -635,9 +643,11 @@ static int tcf_ife_dump(struct sk_buff *
 		pr_info("Failed to dump metalist\n");
 	}
 
+	spin_unlock_bh(&ife->tcf_lock);
 	return skb->len;
 
 nla_put_failure:
+	spin_unlock_bh(&ife->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }