[PATCH net v5 1/2] nfc: replace improper check device_is_registered() in netlink related functions

[Duoming Zhou]

The device_is_registered() in nfc core is used to check whether
nfc device is registered in netlink related functions such as
nfc_fw_download(), nfc_dev_up() and so on. Although device_is_registered()
is protected by device_lock, there is still a race condition between
device_del() and device_is_registered(). The root cause is that
kobject_del() in device_del() is not protected by device_lock.

   (cleanup task)         |     (netlink task)
                          |
nfc_unregister_device     | nfc_fw_download
 device_del               |  device_lock
  ...                     |   if (!device_is_registered)//(1)
  kobject_del//(2)        |   ...
 ...                      |  device_unlock

The device_is_registered() returns the value of state_in_sysfs and
the state_in_sysfs is set to zero in kobject_del(). If we pass check in
position (1), then set zero in position (2). As a result, the check
in position (1) is useless.

This patch uses bool variable instead of device_is_registered() to judge
whether the nfc device is registered, which is well synchronized.

Fixes: 3e256b8f8dfa ("NFC: add nfc subsystem core")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
Changes in v5:
  - Replace device_is_registered() to bool variable.

 include/net/nfc/nfc.h |  1 +
 net/nfc/core.c        | 26 ++++++++++++++------------
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/include/net/nfc/nfc.h b/include/net/nfc/nfc.h
index 5dee575fbe8..7bb4ccb1830 100644
--- a/include/net/nfc/nfc.h
+++ b/include/net/nfc/nfc.h
@@ -167,6 +167,7 @@ struct nfc_dev {
 	int n_targets;
 	int targets_generation;
 	struct device dev;
+	bool dev_register;
 	bool dev_up;
 	bool fw_download_in_progress;
 	u8 rf_mode;
diff --git a/net/nfc/core.c b/net/nfc/core.c
index dc7a2404efd..52147da2286 100644
--- a/net/nfc/core.c
+++ b/net/nfc/core.c
@@ -38,7 +38,7 @@ int nfc_fw_download(struct nfc_dev *dev, const char *firmware_name)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -94,7 +94,7 @@ int nfc_dev_up(struct nfc_dev *dev)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -142,7 +142,7 @@ int nfc_dev_down(struct nfc_dev *dev)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -207,7 +207,7 @@ int nfc_start_poll(struct nfc_dev *dev, u32 im_protocols, u32 tm_protocols)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -246,7 +246,7 @@ int nfc_stop_poll(struct nfc_dev *dev)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -291,7 +291,7 @@ int nfc_dep_link_up(struct nfc_dev *dev, int target_index, u8 comm_mode)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -335,7 +335,7 @@ int nfc_dep_link_down(struct nfc_dev *dev)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -401,7 +401,7 @@ int nfc_activate_target(struct nfc_dev *dev, u32 target_idx, u32 protocol)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -448,7 +448,7 @@ int nfc_deactivate_target(struct nfc_dev *dev, u32 target_idx, u8 mode)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -495,7 +495,7 @@ int nfc_data_exchange(struct nfc_dev *dev, u32 target_idx, struct sk_buff *skb,
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		kfree_skb(skb);
 		goto error;
@@ -552,7 +552,7 @@ int nfc_enable_se(struct nfc_dev *dev, u32 se_idx)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -601,7 +601,7 @@ int nfc_disable_se(struct nfc_dev *dev, u32 se_idx)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (!dev->dev_register) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -1134,6 +1134,7 @@ int nfc_register_device(struct nfc_dev *dev)
 			dev->rfkill = NULL;
 		}
 	}
+	dev->dev_register = true;
 	device_unlock(&dev->dev);
 
 	rc = nfc_genl_device_added(dev);
@@ -1166,6 +1167,7 @@ void nfc_unregister_device(struct nfc_dev *dev)
 		rfkill_unregister(dev->rfkill);
 		rfkill_destroy(dev->rfkill);
 	}
+	dev->dev_register = false;
 	device_unlock(&dev->dev);
 
 	if (dev->ops->check_presence) {
-- 
2.17.1