4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Seunghun Han <kkama...@gmail.com>

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 <kkama...@gmail.com>
Signed-off-by: Borislav Petkov <b...@suse.de>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Tony Luck <tony.l...@intel.com>
Cc: linux-edac <linux-e...@vger.kernel.org>
Cc: sta...@vger.kernel.org
Link: http://lkml.kernel.org/r/20180302202706.9434-1-kkama...@gmail.com
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 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
@@ -57,6 +57,9 @@
 
 static DEFINE_MUTEX(mce_log_mutex);
 
+/* sysfs synchronization */
+static DEFINE_MUTEX(mce_sysfs_mutex);
+
 #define CREATE_TRACE_POINTS
 #include <trace/events/mce.h>
 
@@ -2080,6 +2083,7 @@ 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 */
@@ -2092,6 +2096,8 @@ static ssize_t set_ignore_ce(struct devi
                        on_each_cpu(mce_enable_ce, (void *)1, 1);
                }
        }
+       mutex_unlock(&mce_sysfs_mutex);
+
        return size;
 }
 
@@ -2104,6 +2110,7 @@ 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 */
@@ -2115,6 +2122,8 @@ static ssize_t set_cmci_disabled(struct
                        on_each_cpu(mce_enable_ce, NULL, 1);
                }
        }
+       mutex_unlock(&mce_sysfs_mutex);
+
        return size;
 }
 
@@ -2122,8 +2131,19 @@ 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;
 }
 


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