In the Linux kernel, the following vulnerability has been resolved:
net: ethtool: keep rtnl_lock for the ioctl self test
An offline self test that brings the interface down and back up with netif_close() / netif_open() requires rtnl_lock for both. Since the ethtool IOCTL path became rtnl-optional for ops-locked drivers, the ETHTOOL_TEST ioctl runs holding only the netdev instance lock, so on an ops-locked driver the self test now tears the device down without rtnl_lock.
With lockdep this reproduces deterministically on every offline self test on such a driver; note the sole lock held is the instance lock, not rtnl:
WARNING: suspicious RCU usage net/core/netpoll.c:207 suspicious rcu_dereference_protected() usage! 1 lock held by ethtool/107: #0: (&dev->lock){+.+.}, at: dev_ethtool Call Trace: netpoll_poll_disable __dev_close_many netif_close_many netif_close fbnic_self_test dev_ethtool_locked dev_ethtool dev_ioctl sock_ioctl __x64_sys_ioctl
Without lockdep the same condition trips ASSERT_RTNL() in __dev_close_many() / __dev_open(); that check only samples the global rtnl state, so it can be masked by a concurrent rtnl holder, but the device is still being reconfigured without the lock it requires.
The ethtool self_test is a legacy ioctl-only command, so an ETHTOOL_TEST case is only needed on the ioctl path. Add an opt-in bit for drivers whose self test needs rtnl_lock and set it on the ops-locked drivers whose offline self test tears the interface down and up:
- fbnic (ops-locked via queue_mgmt_ops): fbnic_self_test() offline path uses netif_close() / netif_open(). - bnxt (ops-locked via queue_mgmt_ops): bnxt_self_test() offline path goes through bnxt_close_nic() / bnxt_half_open_nic() / bnxt_half_close_nic() / bnxt_open_nic(), which close and reopen the device.
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