[PATCH v4 1/8] platform/x86: think-lmi: mutex protection around multiple WMI calls

[Mark Pearson <mpearson-lenovo@squebb.ca>]

When an attribute is being changed if the Admin account is enabled, or if a password
is being updated then multiple WMI calls are needed.
Add mutex protection to ensure no race conditions are introduced.

Fixes: b49f72e7f96d ("platform/x86: think-lmi: Certificate authentication support")
Signed-off-by: Mark Pearson <mpearson-lenovo@squebb.ca>
---
Changes in v2:
 - New commit added after review of other patches in series.
Changes in v3:
 - Simplified mutex handling as recommended.
Changes in v4:
 - This was the 5th patch in the series but moved to be first.
 - Added Fixes tag.
 - Improved commit information to be clearer.

 drivers/platform/x86/think-lmi.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/platform/x86/think-lmi.c b/drivers/platform/x86/think-lmi.c
index 1138f770149d..6cf77bc26b05 100644
--- a/drivers/platform/x86/think-lmi.c
+++ b/drivers/platform/x86/think-lmi.c
@@ -14,6 +14,7 @@
 #include <linux/acpi.h>
 #include <linux/errno.h>
 #include <linux/fs.h>
+#include <linux/mutex.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/dmi.h>
@@ -195,6 +196,7 @@ static const char * const level_options[] = {
 };
 static struct think_lmi tlmi_priv;
 static struct class *fw_attr_class;
+static DEFINE_MUTEX(tlmi_mutex);
 
 /* ------ Utility functions ------------*/
 /* Strip out CR if one is present */
@@ -437,6 +439,9 @@ static ssize_t new_password_store(struct kobject *kobj,
 	/* Strip out CR if one is present, setting password won't work if it is present */
 	strip_cr(new_pwd);
 
+	/* Use lock in case multiple WMI operations needed */
+	mutex_lock(&tlmi_mutex);
+
 	pwdlen = strlen(new_pwd);
 	/* pwdlen == 0 is allowed to clear the password */
 	if (pwdlen && ((pwdlen < setting->minlen) || (pwdlen > setting->maxlen))) {
@@ -493,6 +498,7 @@ static ssize_t new_password_store(struct kobject *kobj,
 		kfree(auth_str);
 	}
 out:
+	mutex_unlock(&tlmi_mutex);
 	kfree(new_pwd);
 	return ret ?: count;
 }
@@ -981,6 +987,9 @@ static ssize_t current_value_store(struct kobject *kobj,
 	/* Strip out CR if one is present */
 	strip_cr(new_setting);
 
+	/* Use lock in case multiple WMI operations needed */
+	mutex_lock(&tlmi_mutex);
+
 	/* Check if certificate authentication is enabled and active */
 	if (tlmi_priv.certificate_support && tlmi_priv.pwd_admin->cert_installed) {
 		if (!tlmi_priv.pwd_admin->signature || !tlmi_priv.pwd_admin->save_signature) {
@@ -1039,6 +1048,7 @@ static ssize_t current_value_store(struct kobject *kobj,
 		kobject_uevent(&tlmi_priv.class_dev->kobj, KOBJ_CHANGE);
 	}
 out:
+	mutex_unlock(&tlmi_mutex);
 	kfree(auth_str);
 	kfree(set_str);
 	kfree(new_setting);
-- 
2.40.1