Hi,
Static analysis using Coverity on linux-next has found an issue in
function watchdog_cdev_unregister in source
drivers/watchdog/watchdog_dev.c with the following commit:
commit 7b7d2fdc8c3e3f9fdb3558d674e1eeddc16c7d9e
Author: Curtis Klein <curtis.klein@xxxxxxx>
Date: Wed Feb 3 12:11:30 2021 -0800
watchdog: Add hrtimer-based pretimeout feature
The analysis is as follows:
1084 static void (struct watchdog_device *wdd)
1085 {
1086 struct watchdog_core_data *wd_data = wdd->wd_data;
1087
1088 cdev_device_del(&wd_data->cdev, &wd_data->dev);
1. Condition wdd->id == 0, taking true branch.
1089 if (wdd->id == 0) {
1090 misc_deregister(&watchdog_miscdev);
1091 old_wd_data = NULL;
1092 }
1093
2. Condition watchdog_active(wdd), taking true branch.
3. Condition test_bit(4, &wdd->status), taking true branch.
1094 if (watchdog_active(wdd) &&
1095 test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
1096 watchdog_stop(wdd);
1097 }
1098
1099 mutex_lock(&wd_data->lock);
1100 wd_data->wdd = NULL;
4. assign_zero: Assigning: wdd->wd_data = NULL.
1101 wdd->wd_data = NULL;
1102 mutex_unlock(&wd_data->lock);
1103
1104 hrtimer_cancel(&wd_data->timer);
1105 kthread_cancel_work_sync(&wd_data->work);
Explicit null dereferenced (FORWARD_NULL)
5. var_deref_model: Passing wdd to watchdog_hrtimer_pretimeout_stop,
which dereferences null wdd->wd_data.
1106 watchdog_hrtimer_pretimeout_stop(wdd);
1107
1108 put_device(&wd_data->dev);
1109 }
The call to watchdog_hrtimer_pretimeout_stop dereferences wdd as follows:
41 void watchdog_hrtimer_pretimeout_stop(struct watchdog_device *wdd)
42 {
1. deref_parm_field_in_call: Function hrtimer_cancel dereferences an
offset off wdd->wd_data.
43 hrtimer_cancel(&wdd->wd_data->pretimeout_timer);
44 }
Since wdd->wd_data is set to NULL on line 1101, the call to
watchdog_hrtimer_pretimeout_stop will always trip a null pointer
dereference. Shall we just remove that call?
Colin
