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: Alexandre Belloni <alexandre.belloni@bootlin.com>
diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 9dca53d..e6393e7 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -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;
