[PATCH] drivers: isdn: capi: Fix data-race bug

[madhuparnabhowmik10]

From: Madhuparna Bhowmik <madhuparnabhowmi...@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 <madhuparnabhowmi...@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