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Subject[PATCH 1/2] rtc: ab-b5ze-s3: fix possible race conditions
Date
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>
---
drivers/rtc/rtc-ab-b5ze-s3.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/rtc/rtc-ab-b5ze-s3.c b/drivers/rtc/rtc-ab-b5ze-s3.c
index 8dc451932446..f486912577e7 100644
--- 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);
--
2.17.0
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