[PATCH net] netdevsim: check the driver is bound in new_port/del_port

[Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>]

new_port and del_port are attributes of the bus device, so they stay
reachable after the driver is unbound. nsim_drv_remove() clears
drvdata, yet both handlers pass it straight to priv_to_devlink() and
devl_lock(), which faults on a small negative pointer:

  BUG: unable to handle page fault for address: fffffffffffffeb0
  RIP: 0010:__lock_acquire+0x41/0x2de0 kernel/locking/lockdep.c:5140
  Call Trace:
   lock_acquire+0x115/0x350
   mutex_lock_nested+0x55/0x1d0
   nsim_drv_port_add+0x5a/0x140 drivers/net/netdevsim/dev.c:1760
   new_port_store+0x1a5/0x280 drivers/net/netdevsim/bus.c:96
   kernfs_fop_write_iter+0x3a5/0x540

The nsim_bus_dev->init check does not help: it is only cleared when
the whole device is deleted, not on unbind.

Do what sriov_numvfs already does: take device_lock() so the driver
cannot be unbound underneath us, and return -ENOENT if drvdata is
NULL.

Fixes: 794b2c05ca1c ("netdevsim: extend device attrs to support port addition and deletion")
Reported-by: syzbot+b3fca27eb4005f0111f4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b3fca27eb4005f0111f4
Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
---
Reproduced in QEMU (x86_64, KASAN + lockdep) with the syzbot C repro:
the unpatched kernel oopses in nsim_drv_port_add() right after unbind.
With the patch, the write to new_port returns -ENOENT, a 40s stress of
bind/unbind + new_device/del_device racing with new_port/del_port/
sriov_numvfs runs clean (no splat, no lockdep report, no hung task),
and new_port/del_port still work as before on a bound device.
 drivers/net/netdevsim/bus.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c
index 5c55c308487b..d843b3c985cf 100644
--- a/drivers/net/netdevsim/bus.c
+++ b/drivers/net/netdevsim/bus.c
@@ -93,8 +93,13 @@ new_port_store(struct device *dev, struct device_attribute *attr,
 		return -EINVAL;
 	}
 
-	ret = nsim_drv_port_add(nsim_bus_dev, NSIM_DEV_PORT_TYPE_PF, port_index,
-				addr_set ? eth_addr : NULL);
+	device_lock(dev);
+	ret = -ENOENT;
+	if (dev_get_drvdata(dev))
+		ret = nsim_drv_port_add(nsim_bus_dev, NSIM_DEV_PORT_TYPE_PF,
+					port_index, addr_set ? eth_addr : NULL);
+	device_unlock(dev);
+
 	return ret ? ret : count;
 }
 
@@ -115,7 +120,13 @@ del_port_store(struct device *dev, struct device_attribute *attr,
 	if (ret)
 		return ret;
 
-	ret = nsim_drv_port_del(nsim_bus_dev, NSIM_DEV_PORT_TYPE_PF, port_index);
+	device_lock(dev);
+	ret = -ENOENT;
+	if (dev_get_drvdata(dev))
+		ret = nsim_drv_port_del(nsim_bus_dev, NSIM_DEV_PORT_TYPE_PF,
+					port_index);
+	device_unlock(dev);
+
 	return ret ? ret : count;
 }
 
-- 
2.43.0