[PATCH v4 net-next 4/5] rtnetlink: do not assume RTNL is held in link_master_filtered()

[Eric Dumazet <edumazet@google.com>]

RTNL might be no longer held by the caller in the following patch.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/rtnetlink.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c342b22528e4478a61f22e204a3934ba1a48cb3c..bad036ef7614ffae52a65c447344ac1314f5521b 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2371,22 +2371,24 @@ static struct rtnl_link_ops *linkinfo_to_kind_ops(const struct nlattr *nla,
 static bool link_master_filtered(struct net_device *dev, int master_idx)
 {
 	struct net_device *master;
+	bool res = false;
 
 	if (!master_idx)
 		return false;
 
-	master = netdev_master_upper_dev_get(dev);
+	rcu_read_lock();
+	master = netdev_master_upper_dev_get_rcu(dev);
 
 	/* 0 is already used to denote IFLA_MASTER wasn't passed, therefore need
 	 * another invalid value for ifindex to denote "no master".
 	 */
 	if (master_idx == -1)
-		return !!master;
-
-	if (!master || master->ifindex != master_idx)
-		return true;
+		res = !!master;
+	else if (!master || master->ifindex != master_idx)
+		res = true;
+	rcu_read_unlock();
 
-	return false;
+	return res;
 }
 
 static bool link_kind_filtered(const struct net_device *dev,
-- 
2.54.0.746.g67dd491aae-goog