3 files changed, 28 insertions, 1 deletions

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 06ed6b4e7df5..d5585da14c8a 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -534,6 +534,8 @@ static int _request_firmware(const struct firmware **firmware_p,
                 return 0;
         }
 
+        read_lock_usermodehelper();
+
         if (WARN_ON(usermodehelper_is_disabled())) {
                 dev_err(device, "firmware: %s will not be loaded\n", name);
                 retval = -EBUSY;
@@ -572,6 +574,8 @@ static int _request_firmware(const struct firmware **firmware_p,
         fw_destroy_instance(fw_priv);
 
 out:
+        read_unlock_usermodehelper();
+
         if (retval) {
                 release_firmware(firmware);
                 *firmware_p = NULL;
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index b16f65390734..722f477c4ef7 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -117,5 +117,7 @@ extern void usermodehelper_init(void);
 extern int usermodehelper_disable(void);
 extern void usermodehelper_enable(void);
 extern bool usermodehelper_is_disabled(void);
+extern void read_lock_usermodehelper(void);
+extern void read_unlock_usermodehelper(void);
 
 #endif /* __LINUX_KMOD_H__ */
diff --git a/kernel/kmod.c b/kernel/kmod.c
index a4bea97c75b6..81b4a27261b2 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -36,6 +36,7 @@
 #include <linux/resource.h>
 #include <linux/notifier.h>
 #include <linux/suspend.h>
+#include <linux/rwsem.h>
 #include <asm/uaccess.h>
 
 #include <trace/events/module.h>
@@ -50,6 +51,7 @@ static struct workqueue_struct *khelper_wq;
 static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
 static DEFINE_SPINLOCK(umh_sysctl_lock);
+static DECLARE_RWSEM(umhelper_sem);
 
 #ifdef CONFIG_MODULES
 
@@ -275,6 +277,7 @@ static void __call_usermodehelper(struct work_struct *work)
  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
  * (used for preventing user land processes from being created after the user
  * land has been frozen during a system-wide hibernation or suspend operation).
+ * Should always be manipulated under umhelper_sem acquired for write.
  */
 static int usermodehelper_disabled = 1;
 
@@ -293,6 +296,18 @@ static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
  */
 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 
+void read_lock_usermodehelper(void)
+{
+        down_read(&umhelper_sem);
+}
+EXPORT_SYMBOL_GPL(read_lock_usermodehelper);
+
+void read_unlock_usermodehelper(void)
+{
+        up_read(&umhelper_sem);
+}
+EXPORT_SYMBOL_GPL(read_unlock_usermodehelper);
+
 /**
  * usermodehelper_disable - prevent new helpers from being started
  */
@@ -300,8 +315,10 @@ int usermodehelper_disable(void)
 {
         long retval;
 
+        down_write(&umhelper_sem);
         usermodehelper_disabled = 1;
-        smp_mb();
+        up_write(&umhelper_sem);
+
         /*
          * From now on call_usermodehelper_exec() won't start any new
          * helpers, so it is sufficient if running_helpers turns out to
@@ -314,7 +331,9 @@ int usermodehelper_disable(void)
         if (retval)
                 return 0;
 
+        down_write(&umhelper_sem);
         usermodehelper_disabled = 0;
+        up_write(&umhelper_sem);
         return -EAGAIN;
 }
 
@@ -323,7 +342,9 @@ int usermodehelper_disable(void)
  */
 void usermodehelper_enable(void)
 {
+        down_write(&umhelper_sem);
         usermodehelper_disabled = 0;
+        up_write(&umhelper_sem);
 }
 
 /**