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| author | Guenter Roeck <linux@roeck-us.net> | 2013-04-05 21:22:43 -0700 |
|---|---|---|
| committer | Wim Van Sebroeck <wim@iguana.be> | 2013-05-09 08:13:41 +0200 |
| commit | 60403f7a4d9368d187f79cba5e4672d01df37574 (patch) | |
| tree | c59fab4f8adfbe04244c1fd7bb7ff8073c29f65b | |
| parent | 6330c7070be6783b82025d2bc259db8413c00182 (diff) | |
| download | linux-stable-60403f7a4d9368d187f79cba5e4672d01df37574.tar.gz linux-stable-60403f7a4d9368d187f79cba5e4672d01df37574.tar.bz2 linux-stable-60403f7a4d9368d187f79cba5e4672d01df37574.zip | |
watchdog: Fix race condition in registration code
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 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 <arekm@maven.pl>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Arkadiusz Miskiewicz <arekm@maven.pl>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
| -rw-r--r-- | drivers/watchdog/watchdog_dev.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c index 08b48bbf9f4b..faf4e189fe42 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 */ |