Messages in this thread Patch in this message | | | From | Kamal Mostafa <> | Subject | [PATCH 54/78] watchdog: Fix race condition in registration code | Date | Tue, 28 May 2013 14:20:03 -0700 |
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3.8.13.1 -stable review patch. If anyone has any objections, please let me know.
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From: Guenter Roeck <linux@roeck-us.net>
commit 60403f7a4d9368d187f79cba5e4672d01df37574 upstream.
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> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- 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 ef8edec..05a5310 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -524,6 +524,7 @@ 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) { @@ -532,9 +533,9 @@ 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 */ -- 1.8.1.2
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