2020-11-02 07:46:46

by Wang Wensheng

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

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 <[email protected]>
---
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;
}

/**
--
2.25.0

2020-11-02 08:19:38

by Guenter Roeck

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

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 <[email protected]>
> ---
> 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;
> }
>
> /**
>