[PATCH 4.19 231/346] watchdog: Fix potential dereferencing of null pointer

Greg Kroah-Hartman
2020-12-28T13:33:27Z

From: Wang Wensheng <wangwensheng4@huawei.com>

[ Upstream commit 6f733cb2e7db38f8141b14740bcde577844a03b7 ]

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>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20201109130512.28121-1-wangwensheng4@huawei.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 8b1f37ffb65ac..5c600a3706505 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -246,15 +246,19 @@ 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;
+ }
}
}

--
2.27.0