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From:   madhuparnabhowmik10@gmail.com
To:     isdn@linux-pingi.de, davem@davemloft.net, arnd@arndb.de,
        gregkh@linuxfoundation.org, edumazet@google.com
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        andrianov@ispras.ru, ldv-project@linuxtesting.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Subject: [PATCH] drivers: isdn: capi: Fix data-race bug
Date:   Wed, 22 Jul 2020 22:53:29 +0530
Message-Id: <20200722172329.16727-1-madhuparnabhowmik10@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

In capi_init(), after register_chrdev() the file operation callbacks
can be called. However capinc_tty_init() is called later.
Since capiminors and capinc_tty_driver are initialized in
capinc_tty_init(), their initialization can race with their usage
in various callbacks like in capi_release().

Therefore, call capinc_tty_init() before register_chrdev to avoid
such race conditions.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 drivers/isdn/capi/capi.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/drivers/isdn/capi/capi.c b/drivers/isdn/capi/capi.c
index 85767f52fe3c..7e8ab48a15af 100644
--- a/drivers/isdn/capi/capi.c
+++ b/drivers/isdn/capi/capi.c
@@ -1332,7 +1332,7 @@ static int __init capinc_tty_init(void)
 	return 0;
 }
 
-static void __exit capinc_tty_exit(void)
+static void capinc_tty_exit(void)
 {
 	tty_unregister_driver(capinc_tty_driver);
 	put_tty_driver(capinc_tty_driver);
@@ -1420,29 +1420,28 @@ static int __init capi_init(void)
 	if (ret)
 		return ret;
 
+	if (capinc_tty_init() < 0) {
+		kcapi_exit();
+		return -ENOMEM;
+	}
+
 	major_ret = register_chrdev(capi_major, "capi20", &capi_fops);
 	if (major_ret < 0) {
 		printk(KERN_ERR "capi20: unable to get major %d\n", capi_major);
+		capinc_tty_exit();
 		kcapi_exit();
 		return major_ret;
 	}
 	capi_class = class_create(THIS_MODULE, "capi");
 	if (IS_ERR(capi_class)) {
 		unregister_chrdev(capi_major, "capi20");
+		capinc_tty_exit();
 		kcapi_exit();
 		return PTR_ERR(capi_class);
 	}
 
 	device_create(capi_class, NULL, MKDEV(capi_major, 0), NULL, "capi20");
 
-	if (capinc_tty_init() < 0) {
-		device_destroy(capi_class, MKDEV(capi_major, 0));
-		class_destroy(capi_class);
-		unregister_chrdev(capi_major, "capi20");
-		kcapi_exit();
-		return -ENOMEM;
-	}
-
 	proc_init();
 
 #ifdef CONFIG_ISDN_CAPI_MIDDLEWARE
-- 
2.17.1