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Commit 53d29e0a authored by Alexandre Belloni's avatar Alexandre Belloni
Browse files

rtc: cmos: fix possible race condition 



The probe function is not allowed to fail after registering the RTC 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 register the rtc
as late as possible.

Signed-off-by: default avatarAlexandre Belloni <alexandre.belloni@bootlin.com>
parent 1af7068d

drivers/rtc/rtc-cmos.c

+8 −4
Original line number Diff line number Diff line
@@ -751,8 +751,7 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq) 
	cmos_rtc.dev = dev;

	dev_set_drvdata(dev, &cmos_rtc);



	cmos_rtc.rtc = rtc_device_register(driver_name, dev,

				&cmos_rtc_ops, THIS_MODULE);

	cmos_rtc.rtc = devm_rtc_allocate_device(dev);

	if (IS_ERR(cmos_rtc.rtc)) {

		retval = PTR_ERR(cmos_rtc.rtc);

		goto cleanup0;
@@ -822,6 +821,11 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq) 
		goto cleanup2;

	}



	cmos_rtc.rtc->ops = &cmos_rtc_ops;

	retval = rtc_register_device(cmos_rtc.rtc);

	if (retval)

		goto cleanup3;



	dev_info(dev, "%s%s, %zd bytes nvram%s\n",

		!is_valid_irq(rtc_irq) ? "no alarms" :

			cmos_rtc.mon_alrm ? "alarms up to one year" :
@@ -833,12 +837,13 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq) 


	return 0;



cleanup3:

	sysfs_remove_bin_file(&dev->kobj, &nvram);

cleanup2:

	if (is_valid_irq(rtc_irq))

		free_irq(rtc_irq, cmos_rtc.rtc);

cleanup1:

	cmos_rtc.dev = NULL;

	rtc_device_unregister(cmos_rtc.rtc);

cleanup0:

	if (RTC_IOMAPPED)

		release_region(ports->start, resource_size(ports));
@@ -869,7 +874,6 @@ static void cmos_do_remove(struct device *dev) 
		hpet_unregister_irq_handler(cmos_interrupt);

	}



	rtc_device_unregister(cmos->rtc);

	cmos->rtc = NULL;



	ports = cmos->iomem;