[PATCH net-next v2 5/8] ibmveth: release the pool kobjects when probe fails

[Mingming Cao <mmc@linux.ibm.com>]

If register_netdev() fails in ibmveth_probe(), for example with -EINTR
when the binding task is killed, probe frees the netdev but leaves the
pool%d kobjects embedded in it registered in sysfs. Reading
/sys/devices/vio/<unit>/pool0/num is then a use-after-free, and the
next probe cannot add pool0.

Put the kobjects before freeing the netdev, as ibmveth_remove() does,
on this path and on the netif_set_real_num_tx_queues() one.

The kobjects also have no release(). With CONFIG_DEBUG_KOBJECT_RELEASE,
kobject_put() defers their cleanup, including removing the sysfs files,
to a work item, so free_netdev() can free them first, here and in
remove(). Add a release() that signals a per-pool completion, and wait
for it in both places before free_netdev(). Without that config,
release() runs from kobject_put() and the wait returns at once.

Found by AI-assisted review of the ibmveth multi-queue RX series and
confirmed by code inspection; the release() part was raised by the
Sashiko AI review of the first version. Tested on a POWER10 LPAR with
register_netdev() forced to fail with -EINTR by a test-only module
parameter (not part of this patch): no pool%d directories remain and the
device binds again. No kernel selftests cover ibmveth.

Fixes: 860f242eb534 ("[PATCH] ibmveth change buffer pools dynamically")
Signed-off-by: Mingming Cao <mmc@linux.ibm.com>
---

Changes in v2:
- give the pool kobjects a release() that signals a per-pool
  completion, and wait for it before free_netdev() in probe and
  remove(); with CONFIG_DEBUG_KOBJECT_RELEASE the deferred cleanup
  could run after the free (Sashiko review of v1)
- put the kobjects through one helper, ibmveth_put_pool_kobjs(),
  and an err_put_pools label for both probe failure paths

 drivers/net/ethernet/ibm/ibmveth.c | 52 +++++++++++++++++++++++++-----
 drivers/net/ethernet/ibm/ibmveth.h |  3 ++
 2 files changed, 47 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index 3bac6cabbbb4..a10ebaca9081 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c
@@ -1850,6 +1850,40 @@ static const struct net_device_ops ibmveth_netdev_ops = {
 	.ndo_features_check	= ibmveth_features_check,
 };
 
+/**
+ * ibmveth_pool_kobj_release - Mark a pool kobject finished
+ * @kobj: kobject embedded in the pool
+ *
+ * The pool kobjects live in netdev_priv(), so the last put must wait
+ * for this before free_netdev().
+ */
+static void ibmveth_pool_kobj_release(struct kobject *kobj)
+{
+	struct ibmveth_buff_pool *pool = container_of(kobj,
+						      struct ibmveth_buff_pool,
+						      kobj);
+
+	complete(&pool->released);
+}
+
+/**
+ * ibmveth_put_pool_kobjs - Drop the pool kobjects and wait for release
+ * @adapter: ibmveth adapter
+ *
+ * With CONFIG_DEBUG_KOBJECT_RELEASE the cleanup, including removing the
+ * sysfs files, runs later from a work item in the kobject; wait for it
+ * so free_netdev() cannot free the pools first.
+ */
+static void ibmveth_put_pool_kobjs(struct ibmveth_adapter *adapter)
+{
+	int i;
+
+	for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++)
+		kobject_put(&adapter->rx_buff_pool[i].kobj);
+	for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++)
+		wait_for_completion(&adapter->rx_buff_pool[i].released);
+}
+
 static int ibmveth_probe(struct vio_dev *dev, const struct vio_device_id *id)
 {
 	int rc, i, mac_len;
@@ -1960,6 +1994,7 @@ static int ibmveth_probe(struct vio_dev *dev, const struct vio_device_id *id)
 		ibmveth_init_buffer_pool(&adapter->rx_buff_pool[i], i,
 					 pool_count[i], pool_size[i],
 					 pool_active[i]);
+		init_completion(&adapter->rx_buff_pool[i].released);
 		error = kobject_init_and_add(kobj, &ktype_veth_pool,
 					     &dev->dev.kobj, "pool%d", i);
 		if (!error)
@@ -1971,8 +2006,7 @@ static int ibmveth_probe(struct vio_dev *dev, const struct vio_device_id *id)
 	if (rc) {
 		netdev_dbg(netdev, "failed to set number of tx queues rc=%d\n",
 			   rc);
-		free_netdev(netdev);
-		return rc;
+		goto err_put_pools;
 	}
 	adapter->tx_ltb_size = PAGE_ALIGN(IBMVETH_MAX_TX_BUF_SIZE);
 	for (i = 0; i < IBMVETH_MAX_QUEUES; i++)
@@ -1987,25 +2021,27 @@ static int ibmveth_probe(struct vio_dev *dev, const struct vio_device_id *id)
 
 	if (rc) {
 		netdev_dbg(netdev, "failed to register netdev rc=%d\n", rc);
-		free_netdev(netdev);
-		return rc;
+		goto err_put_pools;
 	}
 
 	netdev_dbg(netdev, "registered\n");
 
 	return 0;
+
+err_put_pools:
+	ibmveth_put_pool_kobjs(adapter);
+	free_netdev(netdev);
+	return rc;
 }
 
 static void ibmveth_remove(struct vio_dev *dev)
 {
 	struct net_device *netdev = dev_get_drvdata(&dev->dev);
 	struct ibmveth_adapter *adapter = netdev_priv(netdev);
-	int i;
 
 	disable_work_sync(&adapter->work);
 
-	for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++)
-		kobject_put(&adapter->rx_buff_pool[i].kobj);
+	ibmveth_put_pool_kobjs(adapter);
 
 	unregister_netdev(netdev);
 
@@ -2181,7 +2217,7 @@ static const struct sysfs_ops veth_pool_ops = {
 };
 
 static struct kobj_type ktype_veth_pool = {
-	.release        = NULL,
+	.release        = ibmveth_pool_kobj_release,
 	.sysfs_ops      = &veth_pool_ops,
 	.default_groups = veth_pool_groups,
 };
diff --git a/drivers/net/ethernet/ibm/ibmveth.h b/drivers/net/ethernet/ibm/ibmveth.h
index 3f2240823f6a..be0939caa328 100644
--- a/drivers/net/ethernet/ibm/ibmveth.h
+++ b/drivers/net/ethernet/ibm/ibmveth.h
@@ -14,6 +14,8 @@
 #ifndef _IBMVETH_H
 #define _IBMVETH_H
 
+#include <linux/completion.h>
+
 /* constants for H_MULTICAST_CTRL */
 #define IbmVethMcastReceptionModifyBit     0x80000UL
 #define IbmVethMcastReceptionEnableBit     0x20000UL
@@ -143,6 +145,7 @@ struct ibmveth_buff_pool {
     struct sk_buff **skbuff;
     int active;
     struct kobject kobj;
+	struct completion released;
 };
 
 struct ibmveth_rx_q {
-- 
2.39.3 (Apple Git-146)