rtc: ab-b5ze-s3: fix possible race conditions

The IRQ is requested before the struct rtc is allocated and registered, but
this struct is used in the IRQ handler. This may lead to a NULL pointer
dereference.

Also, the probe function is not allowed to fail after the RTC is registered
because the following may happen:

CPU0:                                CPU1:
sys_load_module()
 do_init_module()
  do_one_initcall()
   cmos_do_probe()
    rtc_device_register()
     __register_chrdev()
     cdev->owner = struct module*
                                     open("/dev/rtc0")
    rtc_device_unregister()
  module_put()
  free_module()
   module_free(mod->module_core)
   /* struct module *module is now
      freed */
                                      chrdev_open()
                                       spin_lock(cdev_lock)
                                       cdev_get()
                                        try_module_get()
                                         module_is_live()
                                         /* dereferences already
                                            freed struct module* */

Switch to devm_rtc_allocate_device/rtc_register_device to allocate the rtc
before requesting the IRQ and register the RTC as late as possible.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

diff --git a/drivers/rtc/rtc-ab-b5ze-s3.c b/drivers/rtc/rtc-ab-b5ze-s3.c
index 8dc45193244614b1f58fad4ad608bbf9271f6e67..f486912577e7ef358a7a3b90675f4ac7ea72fbc7 100644 (file)
--- a/drivers/rtc/rtc-ab-b5ze-s3.c
+++ b/drivers/rtc/rtc-ab-b5ze-s3.c
@@ -925,6 +925,14 @@ static int abb5zes3_probe(struct i2c_client *client,
        if (ret)
                goto err;
 
+       data->rtc = devm_rtc_allocate_device(dev);
+       ret = PTR_ERR_OR_ZERO(data->rtc);
+       if (ret) {
+               dev_err(dev, "%s: unable to allocate RTC device (%d)\n",
+                       __func__, ret);
+               goto err;
+       }
+
        if (client->irq > 0) {
                ret = devm_request_threaded_irq(dev, client->irq, NULL,
                                                _abb5zes3_rtc_interrupt,
@@ -942,14 +950,7 @@ static int abb5zes3_probe(struct i2c_client *client,
                }
        }
 
-       data->rtc = devm_rtc_device_register(dev, DRV_NAME, &rtc_ops,
-                                            THIS_MODULE);
-       ret = PTR_ERR_OR_ZERO(data->rtc);
-       if (ret) {
-               dev_err(dev, "%s: unable to register RTC device (%d)\n",
-                       __func__, ret);
-               goto err;
-       }
+       data->rtc->ops = &rtc_ops;
 
        /* Enable battery low detection interrupt if battery not already low */
        if (!data->battery_low && data->irq) {
@@ -961,6 +962,8 @@ static int abb5zes3_probe(struct i2c_client *client,
                }
        }
 
+       ret = rtc_register_device(data->rtc);
+
 err:
        if (ret && data && data->irq)
                device_init_wakeup(dev, false);