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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Duoming Zhou <duoming@zju.edu.cn>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.4 20/52] nfc: replace improper check device_is_registered() in netlink related functions
Date:   Tue, 10 May 2022 15:07:49 +0200
Message-Id: <20220510130730.446023203@linuxfoundation.org>
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From: Duoming Zhou <duoming@zju.edu.cn>

commit da5c0f119203ad9728920456a0f52a6d850c01cd upstream.

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@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/nfc/core.c |   29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

--- a/net/nfc/core.c
+++ b/net/nfc/core.c
@@ -38,7 +38,7 @@ int nfc_fw_download(struct nfc_dev *dev,
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		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->shutting_down) {
 		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->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -206,7 +206,7 @@ int nfc_start_poll(struct nfc_dev *dev,
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -245,7 +245,7 @@ int nfc_stop_poll(struct nfc_dev *dev)
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -290,7 +290,7 @@ int nfc_dep_link_up(struct nfc_dev *dev,
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -334,7 +334,7 @@ int nfc_dep_link_down(struct nfc_dev *de
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -400,7 +400,7 @@ int nfc_activate_target(struct nfc_dev *
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -446,7 +446,7 @@ int nfc_deactivate_target(struct nfc_dev
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -493,7 +493,7 @@ int nfc_data_exchange(struct nfc_dev *de
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		kfree_skb(skb);
 		goto error;
@@ -550,7 +550,7 @@ int nfc_enable_se(struct nfc_dev *dev, u
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -599,7 +599,7 @@ int nfc_disable_se(struct nfc_dev *dev,
 
 	device_lock(&dev->dev);
 
-	if (!device_is_registered(&dev->dev)) {
+	if (dev->shutting_down) {
 		rc = -ENODEV;
 		goto error;
 	}
@@ -1127,6 +1127,7 @@ int nfc_register_device(struct nfc_dev *
 			dev->rfkill = NULL;
 		}
 	}
+	dev->shutting_down = false;
 	device_unlock(&dev->dev);
 
 	rc = nfc_genl_device_added(dev);
@@ -1159,12 +1160,10 @@ void nfc_unregister_device(struct nfc_de
 		rfkill_unregister(dev->rfkill);
 		rfkill_destroy(dev->rfkill);
 	}
+	dev->shutting_down = true;
 	device_unlock(&dev->dev);
 
 	if (dev->ops->check_presence) {
-		device_lock(&dev->dev);
-		dev->shutting_down = true;
-		device_unlock(&dev->dev);
 		del_timer_sync(&dev->check_pres_timer);
 		cancel_work_sync(&dev->check_pres_work);
 	}