From 8614ddef82139d08234dbf681188f9bcddae9f03 Mon Sep 17 00:00:00 2001 From: Ulrich Obergfell Date: Thu, 5 Nov 2015 18:44:50 -0800 Subject: kernel/watchdog.c: avoid races between /proc handlers and CPU hotplug The handler functions for watchdog parameters in /proc/sys/kernel do not protect themselves against races with CPU hotplug. Hence, theoretically it is possible that a new watchdog thread is started on a hotplugged CPU while a parameter is being modified, and the thread could thus use a parameter value that is 'in transition'. For example, if 'watchdog_thresh' is being set to zero (note: this disables the lockup detectors) the thread would erroneously use the value zero as the sample period. To avoid such races and to keep the /proc handler code consistent, call {get|put}_online_cpus() in proc_watchdog_common() {get|put}_online_cpus() in proc_watchdog_thresh() {get|put}_online_cpus() in proc_watchdog_cpumask() Signed-off-by: Ulrich Obergfell Acked-by: Don Zickus Reviewed-by: Aaron Tomlin Cc: Ulrich Obergfell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/watchdog.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 7357842da933..13fdda1a4c91 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -857,6 +857,7 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write, int err, old, new; int *watchdog_param = (int *)table->data; + get_online_cpus(); mutex_lock(&watchdog_proc_mutex); if (watchdog_suspended) { @@ -908,6 +909,7 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write, } out: mutex_unlock(&watchdog_proc_mutex); + put_online_cpus(); return err; } @@ -949,6 +951,7 @@ int proc_watchdog_thresh(struct ctl_table *table, int write, { int err, old; + get_online_cpus(); mutex_lock(&watchdog_proc_mutex); if (watchdog_suspended) { @@ -974,6 +977,7 @@ int proc_watchdog_thresh(struct ctl_table *table, int write, } out: mutex_unlock(&watchdog_proc_mutex); + put_online_cpus(); return err; } @@ -988,6 +992,7 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write, { int err; + get_online_cpus(); mutex_lock(&watchdog_proc_mutex); if (watchdog_suspended) { @@ -1015,6 +1020,7 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write, } out: mutex_unlock(&watchdog_proc_mutex); + put_online_cpus(); return err; } -- cgit v1.2.3