3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Seunghun Han <kkamagui@xxxxxxxxx> commit b3b7c4795ccab5be71f080774c45bbbcc75c2aaf upstream. The check_interval file in /sys/devices/system/machinecheck/machinecheck<cpu number> directory is a global timer value for MCE polling. If it is changed by one CPU, mce_restart() broadcasts the event to other CPUs to delete and restart the MCE polling timer and __mcheck_cpu_init_timer() reinitializes the mce_timer variable. If more than one CPU writes a specific value to the check_interval file concurrently, mce_timer is not protected from such concurrent accesses and all kinds of explosions happen. Since only root can write to those sysfs variables, the issue is not a big deal security-wise. However, concurrent writes to these configuration variables is void of reason so the proper thing to do is to serialize the access with a mutex. Boris: - Make store_int_with_restart() use device_store_ulong() to filter out negative intervals - Limit min interval to 1 second - Correct locking - Massage commit message Signed-off-by: Seunghun Han <kkamagui@xxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Tony Luck <tony.luck@xxxxxxxxx> Cc: linux-edac <linux-edac@xxxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: http://lkml.kernel.org/r/20180302202706.9434-1-kkamagui@xxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/cpu/mcheck/mce.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -56,6 +56,9 @@ static DEFINE_MUTEX(mce_chrdev_read_mute rcu_read_lock_sched_held() || \ lockdep_is_held(&mce_chrdev_read_mutex)) +/* sysfs synchronization */ +static DEFINE_MUTEX(mce_sysfs_mutex); + #define CREATE_TRACE_POINTS #include <trace/events/mce.h> @@ -2183,6 +2186,7 @@ static ssize_t set_ignore_ce(struct devi if (kstrtou64(buf, 0, &new) < 0) return -EINVAL; + mutex_lock(&mce_sysfs_mutex); if (mca_cfg.ignore_ce ^ !!new) { if (new) { /* disable ce features */ @@ -2195,6 +2199,8 @@ static ssize_t set_ignore_ce(struct devi on_each_cpu(mce_enable_ce, (void *)1, 1); } } + mutex_unlock(&mce_sysfs_mutex); + return size; } @@ -2207,6 +2213,7 @@ static ssize_t set_cmci_disabled(struct if (kstrtou64(buf, 0, &new) < 0) return -EINVAL; + mutex_lock(&mce_sysfs_mutex); if (mca_cfg.cmci_disabled ^ !!new) { if (new) { /* disable cmci */ @@ -2218,6 +2225,8 @@ static ssize_t set_cmci_disabled(struct on_each_cpu(mce_enable_ce, NULL, 1); } } + mutex_unlock(&mce_sysfs_mutex); + return size; } @@ -2225,8 +2234,19 @@ static ssize_t store_int_with_restart(st struct device_attribute *attr, const char *buf, size_t size) { - ssize_t ret = device_store_int(s, attr, buf, size); + unsigned long old_check_interval = check_interval; + ssize_t ret = device_store_ulong(s, attr, buf, size); + + if (check_interval == old_check_interval) + return ret; + + if (check_interval < 1) + check_interval = 1; + + mutex_lock(&mce_sysfs_mutex); mce_restart(); + mutex_unlock(&mce_sysfs_mutex); + return ret; }