2020-11-09 13:38:14

by Wang Wensheng

Subject: [PATCH -next v4] 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 | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
index 423844757812..0e9a99559609 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -267,15 +267,19 @@ 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;
-
- 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;
+ if (!wdd->ops->stop)
+ pr_warn("watchdog%d: stop_on_reboot not supported\n", wdd->id);
+ else {
+ 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;
+ }
}
}

--
2.25.0

2020-11-10 16:05:01

by Guenter Roeck

Subject: Re: [PATCH -next v4] watchdog: Fix potential dereferencing of null pointer

On Mon, Nov 09, 2020 at 01:05:12PM +0000, 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.
>
> Fixes: d0684c8a9354 ("watchdog: Make stop function optional")
> Signed-off-by: Wang Wensheng <[email protected]>

Reviewed-by: Guenter Roeck <[email protected]>

> ---
> drivers/watchdog/watchdog_core.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 423844757812..0e9a99559609 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -267,15 +267,19 @@ 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;
> -
> - 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;
> + if (!wdd->ops->stop)
> + pr_warn("watchdog%d: stop_on_reboot not supported\n", wdd->id);
> + else {
> + 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;
> + }
> }
> }
>
> --
> 2.25.0
>