[-next] watchdog: Fix potential dereferencing of null pointer

Message ID 20201102074413.69552-1-wangwensheng4@huawei.com
State New
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Series
  • [-next] watchdog: Fix potential dereferencing of null pointer
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Commit Message

Wang Wensheng Nov. 2, 2020, 7:44 a.m.
A reboot notifier, which stops the WDT by calling the stop hook without
any check, would be registered when we set WDOG_STOP_ON_REBOOT flag.

Howerer we allow the WDT driver to omit the stop hook since commit
"d0684c8a93549" ("watchdog: Make stop function optional") and provide
a module parameter for user that controls the WDOG_STOP_ON_REBOOT flag
in commit 9232c80659e94 ("watchdog: Add stop_on_reboot parameter to
control reboot policy"). Together that commits make user potential to
insert a watchdog driver that don't provide a stop hook but with the
stop_on_reboot parameter set, then dereferencing of null pointer occurs
on system reboot.

Check the stop hook before registering the reboot notifier to fix the
issue.

Fixes: d0684c8a9354 ("watchdog: Make stop function optional")
Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
---
 drivers/watchdog/watchdog_core.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

Comments

Guenter Roeck Nov. 2, 2020, 8:15 a.m. | #1
On 11/1/20 11:44 PM, Wang Wensheng wrote:
> A reboot notifier, which stops the WDT by calling the stop hook without

> any check, would be registered when we set WDOG_STOP_ON_REBOOT flag.

> 

> Howerer we allow the WDT driver to omit the stop hook since commit

> "d0684c8a93549" ("watchdog: Make stop function optional") and provide

> a module parameter for user that controls the WDOG_STOP_ON_REBOOT flag

> in commit 9232c80659e94 ("watchdog: Add stop_on_reboot parameter to

> control reboot policy"). Together that commits make user potential to

> insert a watchdog driver that don't provide a stop hook but with the

> stop_on_reboot parameter set, then dereferencing of null pointer occurs

> on system reboot.

> 

> Check the stop hook before registering the reboot notifier to fix the

> issue.

> 


This does a bit more: It also cleans up error handling. Which makes sense,
but should be done in a second patch.

Guenter

> Fixes: d0684c8a9354 ("watchdog: Make stop function optional")

> Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>

> ---

>  drivers/watchdog/watchdog_core.c | 23 +++++++++++++++--------

>  1 file changed, 15 insertions(+), 8 deletions(-)

> 

> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c

> index 423844757812..5269761ba072 100644

> --- a/drivers/watchdog/watchdog_core.c

> +++ b/drivers/watchdog/watchdog_core.c

> @@ -252,10 +252,8 @@ static int __watchdog_register_device(struct watchdog_device *wdd)

>  		wdd->id = id;

>  

>  		ret = watchdog_dev_register(wdd);

> -		if (ret) {

> -			ida_simple_remove(&watchdog_ida, id);

> -			return ret;

> -		}

> +		if (ret)

> +			goto id_remove;

>  	}

>  

>  	/* Module parameter to force watchdog policy on reboot. */

> @@ -267,15 +265,17 @@ static int __watchdog_register_device(struct watchdog_device *wdd)

>  	}

>  

>  	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {

> -		wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;

> +		if (!wdd->ops->stop) {

> +			ret = -EINVAL;

> +			goto dev_unregister;

> +		}

>  

> +		wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;

>  		ret = register_reboot_notifier(&wdd->reboot_nb);

>  		if (ret) {

>  			pr_err("watchdog%d: Cannot register reboot notifier (%d)\n",

>  			       wdd->id, ret);

> -			watchdog_dev_unregister(wdd);

> -			ida_simple_remove(&watchdog_ida, id);

> -			return ret;

> +			goto dev_unregister;

>  		}

>  	}

>  

> @@ -289,6 +289,13 @@ static int __watchdog_register_device(struct watchdog_device *wdd)

>  	}

>  

>  	return 0;

> +

> +dev_unregister:

> +	watchdog_dev_unregister(wdd);

> +id_remove:

> +	ida_simple_remove(&watchdog_ida, id);

> +

> +	return ret;

>  }

>  

>  /**

>

Patch

diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
index 423844757812..5269761ba072 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -252,10 +252,8 @@  static int __watchdog_register_device(struct watchdog_device *wdd)
 		wdd->id = id;
 
 		ret = watchdog_dev_register(wdd);
-		if (ret) {
-			ida_simple_remove(&watchdog_ida, id);
-			return ret;
-		}
+		if (ret)
+			goto id_remove;
 	}
 
 	/* Module parameter to force watchdog policy on reboot. */
@@ -267,15 +265,17 @@  static int __watchdog_register_device(struct watchdog_device *wdd)
 	}
 
 	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
-		wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
+		if (!wdd->ops->stop) {
+			ret = -EINVAL;
+			goto dev_unregister;
+		}
 
+		wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
 		ret = register_reboot_notifier(&wdd->reboot_nb);
 		if (ret) {
 			pr_err("watchdog%d: Cannot register reboot notifier (%d)\n",
 			       wdd->id, ret);
-			watchdog_dev_unregister(wdd);
-			ida_simple_remove(&watchdog_ida, id);
-			return ret;
+			goto dev_unregister;
 		}
 	}
 
@@ -289,6 +289,13 @@  static int __watchdog_register_device(struct watchdog_device *wdd)
 	}
 
 	return 0;
+
+dev_unregister:
+	watchdog_dev_unregister(wdd);
+id_remove:
+	ida_simple_remove(&watchdog_ida, id);
+
+	return ret;
 }
 
 /**