bonding: hold ops lock around get_link

syzbot reports a case of ethtool_ops->get_link being called without
ops lock:

 ethtool_op_get_link+0x15/0x60 net/ethtool/ioctl.c:63
 bond_check_dev_link+0x1fb/0x4b0 drivers/net/bonding/bond_main.c:864
 bond_miimon_inspect drivers/net/bonding/bond_main.c:2734 [inline]
 bond_mii_monitor+0x49d/0x3170 drivers/net/bonding/bond_main.c:2956
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xac3/0x18e0 kernel/workqueue.c:3319
 worker_thread+0x870/0xd50 kernel/workqueue.c:3400
 kthread+0x7b7/0x940 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Commit 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")
changed to lockless __linkwatch_sync_dev in ethtool_op_get_link.
All paths except bonding are coming via locked ioctl. Add necessary
locking to bonding.

Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reported-by: syzbot+48c14f61594bdfadb086@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=48c14f61594bdfadb086
Fixes: 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250410161117.3519250-1-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 950d8e4d86f8b4e9f7a620f315be675f44080f27..8ea183da8d5398ee5facd0aa103f8c3bd2913287 100644 (file)
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -850,8 +850,9 @@ static int bond_check_dev_link(struct bonding *bond,
                               struct net_device *slave_dev, int reporting)
 {
        const struct net_device_ops *slave_ops = slave_dev->netdev_ops;
-       struct ifreq ifr;
        struct mii_ioctl_data *mii;
+       struct ifreq ifr;
+       int ret;
 
        if (!reporting && !netif_running(slave_dev))
                return 0;
@@ -860,9 +861,13 @@ static int bond_check_dev_link(struct bonding *bond,
                return netif_carrier_ok(slave_dev) ? BMSR_LSTATUS : 0;
 
        /* Try to get link status using Ethtool first. */
-       if (slave_dev->ethtool_ops->get_link)
-               return slave_dev->ethtool_ops->get_link(slave_dev) ?
-                       BMSR_LSTATUS : 0;
+       if (slave_dev->ethtool_ops->get_link) {
+               netdev_lock_ops(slave_dev);
+               ret = slave_dev->ethtool_ops->get_link(slave_dev);
+               netdev_unlock_ops(slave_dev);
+
+               return ret ? BMSR_LSTATUS : 0;
+       }
 
        /* Ethtool can't be used, fallback to MII ioctls. */
        if (slave_ops->ndo_eth_ioctl) {