netdev - [PATCH net] bonding: fix lockdep splat in bond_miimon

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Date:   Tue, 20 Dec 2022 13:08:31 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        Eric Dumazet <edumazet@...gle.com>,
        syzbot <syzkaller@...glegroups.com>,
        Hangbin Liu <liuhangbin@...il.com>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>
Subject: [PATCH net] bonding: fix lockdep splat in bond_miimon_commit()

bond_miimon_commit() is run while RTNL is held, not RCU.

WARNING: suspicious RCU usage
6.1.0-syzkaller-09671-g89529367293c #0 Not tainted
-----------------------------
drivers/net/bonding/bond_main.c:2704 suspicious rcu_dereference_check() usage!

Fixes: e95cc44763a4 ("bonding: do failover when high prio link up")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
Cc: Hangbin Liu <liuhangbin@...il.com>
Cc: Jay Vosburgh <j.vosburgh@...il.com>
Cc: Veaceslav Falico <vfalico@...il.com>
Cc: Andy Gospodarek <andy@...yhouse.net>
---
 drivers/net/bonding/bond_main.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index b4c65783960a5aa14de5d64aeea190f02a04be44..0363ce597661422b82a7d33ef001151b275f9ada 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2654,10 +2654,12 @@ static void bond_miimon_link_change(struct bonding *bond,
 
 static void bond_miimon_commit(struct bonding *bond)
 {
-	struct slave *slave, *primary;
+	struct slave *slave, *primary, *active;
 	bool do_failover = false;
 	struct list_head *iter;
 
+	ASSERT_RTNL();
+
 	bond_for_each_slave(bond, slave, iter) {
 		switch (slave->link_new_state) {
 		case BOND_LINK_NOCHANGE:
@@ -2700,8 +2702,8 @@ static void bond_miimon_commit(struct bonding *bond)
 
 			bond_miimon_link_change(bond, slave, BOND_LINK_UP);
 
-			if (!rcu_access_pointer(bond->curr_active_slave) || slave == primary ||
-			    slave->prio > rcu_dereference(bond->curr_active_slave)->prio)
+			active = rtnl_dereference(bond->curr_active_slave);
+			if (!active || slave == primary || slave->prio > active->prio)
 				do_failover = true;
 
 			continue;
-- 
2.39.0.314.g84b9a713c41-goog