A race condition exists when registering the first watchdog device.
Sequence of events:
- watchdog_register_device calls watchdog_dev_register
- watchdog_dev_register creates the watchdog misc device by calling
misc_register.
At that time, the matching character device (/dev/watchdog0) does not yet
exist, and old_wdd is not set either.
- Userspace gets an event and opens /dev/watchdog
- watchdog_open is called and sets sets wdd = old_wdd, which is still NULL,
and tries to dereference it. This causes the kernel to panic.
Seen with systemd trying to open /dev/watchdog immediately after
it was created.
Reported-by: Arkadiusz Miskiewicz <a.miskiewicz@xxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
Arkadiusz,
would be great if you can test this in your system.
drivers/watchdog/watchdog_dev.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 08b48bb..faf4e18 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -523,6 +523,7 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
int err, devno;
if (watchdog->id == 0) {
+ old_wdd = watchdog;
watchdog_miscdev.parent = watchdog->parent;
err = misc_register(&watchdog_miscdev);
if (err != 0) {
@@ -531,9 +532,9 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
if (err == -EBUSY)
pr_err("%s: a legacy watchdog module is probably present.\n",
watchdog->info->identity);
+ old_wdd = NULL;
return err;
}
- old_wdd = watchdog;
}
/* Fill in the data structures */
--
1.7.9.7
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