[PATCH v2] net/smc: hold a reference on net_device returned by pnet_find_base_ndev()

[Atharva Vartak <atharva.a.vartak@gmail.com>]

pnet_find_base_ndev() resolves the base net_device for stacked devices
under RTNL, then drops the lock and returns the raw pointer without
taking a reference.  All three callers dereference the pointer after
RTNL has been released, creating a use-after-free window if the device
is concurrently unregistered.

Take a reference with netdev_hold() before dropping RTNL and add the
matching netdev_put() in every return path of the three callers:

  - smc_pnet_add_eth()
  - smc_pnet_find_roce_by_pnetid()
  - smc_pnet_find_ism_by_pnetid()

Fixes: 0afff91c6f5e ("net/smc: add pnetid support")
Fixes: 1619f770589a ("net/smc: add pnetid support for SMC-D and ISM")
Cc: "D. Wythe" <alibuda@linux.alibaba.com>
Cc: Dust Li <dust.li@linux.alibaba.com>
Cc: Sidraya Jayagond <sidraya@linux.ibm.com>
Cc: Mahanta Jambigi <mjambigi@linux.ibm.com>
Cc: Tony Lu <tonylu@linux.alibaba.com>
Cc: Wen Gu <guwen@linux.alibaba.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: linux-rdma@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Atharva Vartak <atharva.a.vartak@gmail.com>
---
v2: use netdev_hold()/netdev_put() with a netdevice_tracker instead of
    the deprecated dev_hold()/dev_put() (Jakub Kicinski).
v1: https://lore.kernel.org/netdev/6aba080c.b933486d.297b72.5042@mx.google.com/

 net/smc/smc_pnet.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/net/smc/smc_pnet.c b/net/smc/smc_pnet.c
index ff9c9c35cc2f..61ef1d697eee 100644
--- a/net/smc/smc_pnet.c
+++ b/net/smc/smc_pnet.c
@@ -30,7 +30,8 @@
 #include "smc_core.h"
 
 static struct net_device *__pnet_find_base_ndev(struct net_device *ndev);
-static struct net_device *pnet_find_base_ndev(struct net_device *ndev);
+static struct net_device *pnet_find_base_ndev(struct net_device *ndev,
+					      netdevice_tracker *tracker);
 
 static const struct nla_policy smc_pnet_policy[SMC_PNETID_MAX + 1] = {
 	[SMC_PNETID_NAME] = {
@@ -356,6 +357,7 @@ static int smc_pnet_add_eth(struct smc_pnettable *pnettable, struct net *net,
 	struct smc_pnetentry *tmp_pe, *new_pe;
 	struct net_device *ndev, *base_ndev;
 	u8 ndev_pnetid[SMC_MAX_PNETID_LEN];
+	netdevice_tracker base_tracker;
 	bool new_netdev;
 	int rc;
 
@@ -365,10 +367,13 @@ static int smc_pnet_add_eth(struct smc_pnettable *pnettable, struct net *net,
 	rc = -EEXIST;
 	ndev = dev_get_by_name(net, eth_name);	/* dev_hold() */
 	if (ndev) {
-		base_ndev = pnet_find_base_ndev(ndev);
+		base_ndev = pnet_find_base_ndev(ndev, &base_tracker);
 		if (!smc_pnetid_by_dev_port(base_ndev->dev.parent,
-					    base_ndev->dev_port, ndev_pnetid))
+					    base_ndev->dev_port, ndev_pnetid)) {
+			netdev_put(base_ndev, &base_tracker);
 			goto out_put;
+		}
+		netdev_put(base_ndev, &base_tracker);
 	}
 
 	/* add a new netdev entry to the pnet table if there isn't one */
@@ -945,10 +950,13 @@ static struct net_device *__pnet_find_base_ndev(struct net_device *ndev)
  * (for instance with bonding slaves), just the first device
  * is used to reach a base device.
  */
-static struct net_device *pnet_find_base_ndev(struct net_device *ndev)
+static struct net_device *pnet_find_base_ndev(struct net_device *ndev,
+					      netdevice_tracker *tracker)
 {
 	rtnl_lock();
 	ndev = __pnet_find_base_ndev(ndev);
+	/* keep ndev alive after dropping RTNL, callers must netdev_put() */
+	netdev_hold(ndev, tracker, GFP_KERNEL);
 	rtnl_unlock();
 	return ndev;
 }
@@ -1085,17 +1093,20 @@ static void smc_pnet_find_roce_by_pnetid(struct net_device *ndev,
 {
 	u8 ndev_pnetid[SMC_MAX_PNETID_LEN];
 	struct net_device *base_ndev;
+	netdevice_tracker base_tracker;
 	struct net *net;
 
-	base_ndev = pnet_find_base_ndev(ndev);
+	base_ndev = pnet_find_base_ndev(ndev, &base_tracker);
 	net = dev_net(ndev);
 	if (smc_pnetid_by_dev_port(base_ndev->dev.parent, base_ndev->dev_port,
 				   ndev_pnetid) &&
 	    smc_pnet_find_ndev_pnetid_by_table(base_ndev, ndev_pnetid) &&
 	    smc_pnet_find_ndev_pnetid_by_table(ndev, ndev_pnetid)) {
 		smc_pnet_find_rdma_dev(base_ndev, ini);
+		netdev_put(base_ndev, &base_tracker);
 		return; /* pnetid could not be determined */
 	}
+	netdev_put(base_ndev, &base_tracker);
 	_smc_pnet_find_roce_by_pnetid(ndev_pnetid, ini, NULL, net);
 }
 
@@ -1103,13 +1114,16 @@ static void smc_pnet_find_ism_by_pnetid(struct net_device *ndev,
 					struct smc_init_info *ini)
 {
 	u8 ndev_pnetid[SMC_MAX_PNETID_LEN];
+	netdevice_tracker base_tracker;
 	struct smcd_dev *ismdev;
 
-	ndev = pnet_find_base_ndev(ndev);
+	ndev = pnet_find_base_ndev(ndev, &base_tracker);
 	if (smc_pnetid_by_dev_port(ndev->dev.parent, ndev->dev_port,
 				   ndev_pnetid) &&
-	    smc_pnet_find_ndev_pnetid_by_table(ndev, ndev_pnetid))
+	    smc_pnet_find_ndev_pnetid_by_table(ndev, ndev_pnetid)) {
+		netdev_put(ndev, &base_tracker);
 		return; /* pnetid could not be determined */
+	}
 
 	mutex_lock(&smcd_dev_list.mutex);
 	list_for_each_entry(ismdev, &smcd_dev_list.list, list) {
@@ -1123,6 +1137,7 @@ static void smc_pnet_find_ism_by_pnetid(struct net_device *ndev,
 		}
 	}
 	mutex_unlock(&smcd_dev_list.mutex);
+	netdev_put(ndev, &base_tracker);
 }
 
 /* PNET table analysis for a given sock:
-- 
2.56.0