1 files changed, 147 insertions, 68 deletions

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 1500cfd799a7..32a8a867f7f8 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -42,6 +42,7 @@
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/random.h>
+#include <linux/err.h>
 #include <asm/uaccess.h>
 
 
@@ -53,7 +54,10 @@
 static struct hwrng *current_rng;
 static struct task_struct *hwrng_fill;
 static LIST_HEAD(rng_list);
+/* Protects rng_list and current_rng */
 static DEFINE_MUTEX(rng_mutex);
+/* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */
+static DEFINE_MUTEX(reading_mutex);
 static int data_avail;
 static u8 *rng_buffer, *rng_fillbuf;
 static unsigned short current_quality;
@@ -66,6 +70,8 @@ module_param(default_quality, ushort, 0644);
 MODULE_PARM_DESC(default_quality,
 		 "default entropy content of hwrng per mill");
 
+static void drop_current_rng(void);
+static int hwrng_init(struct hwrng *rng);
 static void start_khwrngd(void);
 
 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
@@ -81,13 +87,83 @@ static void add_early_randomness(struct hwrng *rng)
 	unsigned char bytes[16];
 	int bytes_read;
 
+	mutex_lock(&reading_mutex);
 	bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
+	mutex_unlock(&reading_mutex);
 	if (bytes_read > 0)
 		add_device_randomness(bytes, bytes_read);
 }
 
-static inline int hwrng_init(struct hwrng *rng)
+static inline void cleanup_rng(struct kref *kref)
 {
+	struct hwrng *rng = container_of(kref, struct hwrng, ref);
+
+	if (rng->cleanup)
+		rng->cleanup(rng);
+
+	complete(&rng->cleanup_done);
+}
+
+static int set_current_rng(struct hwrng *rng)
+{
+	int err;
+
+	BUG_ON(!mutex_is_locked(&rng_mutex));
+
+	err = hwrng_init(rng);
+	if (err)
+		return err;
+
+	drop_current_rng();
+	current_rng = rng;
+
+	return 0;
+}
+
+static void drop_current_rng(void)
+{
+	BUG_ON(!mutex_is_locked(&rng_mutex));
+	if (!current_rng)
+		return;
+
+	/* decrease last reference for triggering the cleanup */
+	kref_put(&current_rng->ref, cleanup_rng);
+	current_rng = NULL;
+}
+
+/* Returns ERR_PTR(), NULL or refcounted hwrng */
+static struct hwrng *get_current_rng(void)
+{
+	struct hwrng *rng;
+
+	if (mutex_lock_interruptible(&rng_mutex))
+		return ERR_PTR(-ERESTARTSYS);
+
+	rng = current_rng;
+	if (rng)
+		kref_get(&rng->ref);
+
+	mutex_unlock(&rng_mutex);
+	return rng;
+}
+
+static void put_rng(struct hwrng *rng)
+{
+	/*
+	 * Hold rng_mutex here so we serialize in case they set_current_rng
+	 * on rng again immediately.
+	 */
+	mutex_lock(&rng_mutex);
+	if (rng)
+		kref_put(&rng->ref, cleanup_rng);
+	mutex_unlock(&rng_mutex);
+}
+
+static int hwrng_init(struct hwrng *rng)
+{
+	if (kref_get_unless_zero(&rng->ref))
+		goto skip_init;
+
 	if (rng->init) {
 		int ret;
 
@@ -95,6 +171,11 @@ static inline int hwrng_init(struct hwrng *rng)
 		if (ret)
 			return ret;
 	}
+
+	kref_init(&rng->ref);
+	reinit_completion(&rng->cleanup_done);
+
+skip_init:
 	add_early_randomness(rng);
 
 	current_quality = rng->quality ? : default_quality;
@@ -108,12 +189,6 @@ static inline int hwrng_init(struct hwrng *rng)
 	return 0;
 }
 
-static inline void hwrng_cleanup(struct hwrng *rng)
-{
-	if (rng && rng->cleanup)
-		rng->cleanup(rng);
-}
-
 static int rng_dev_open(struct inode *inode, struct file *filp)
 {
 	/* enforce read-only access to this chrdev */
@@ -128,6 +203,7 @@ static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
 			int wait) {
 	int present;
 
+	BUG_ON(!mutex_is_locked(&reading_mutex));
 	if (rng->read)
 		return rng->read(rng, (void *)buffer, size, wait);
 
@@ -148,25 +224,27 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 	ssize_t ret = 0;
 	int err = 0;
 	int bytes_read, len;
+	struct hwrng *rng;
 
 	while (size) {
-		if (mutex_lock_interruptible(&rng_mutex)) {
-			err = -ERESTARTSYS;
+		rng = get_current_rng();
+		if (IS_ERR(rng)) {
+			err = PTR_ERR(rng);
 			goto out;
 		}
-
-		if (!current_rng) {
+		if (!rng) {
 			err = -ENODEV;
-			goto out_unlock;
+			goto out;
 		}
 
+		mutex_lock(&reading_mutex);
 		if (!data_avail) {
-			bytes_read = rng_get_data(current_rng, rng_buffer,
+			bytes_read = rng_get_data(rng, rng_buffer,
 				rng_buffer_size(),
 				!(filp->f_flags & O_NONBLOCK));
 			if (bytes_read < 0) {
 				err = bytes_read;
-				goto out_unlock;
+				goto out_unlock_reading;
 			}
 			data_avail = bytes_read;
 		}
@@ -174,7 +252,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 		if (!data_avail) {
 			if (filp->f_flags & O_NONBLOCK) {
 				err = -EAGAIN;
-				goto out_unlock;
+				goto out_unlock_reading;
 			}
 		} else {
 			len = data_avail;
@@ -186,14 +264,15 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 			if (copy_to_user(buf + ret, rng_buffer + data_avail,
 								len)) {
 				err = -EFAULT;
-				goto out_unlock;
+				goto out_unlock_reading;
 			}
 
 			size -= len;
 			ret += len;
 		}
 
-		mutex_unlock(&rng_mutex);
+		mutex_unlock(&reading_mutex);
+		put_rng(rng);
 
 		if (need_resched())
 			schedule_timeout_interruptible(1);
@@ -205,8 +284,10 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 	}
 out:
 	return ret ? : err;
-out_unlock:
-	mutex_unlock(&rng_mutex);
+
+out_unlock_reading:
+	mutex_unlock(&reading_mutex);
+	put_rng(rng);
 	goto out;
 }
 
@@ -239,16 +320,9 @@ static ssize_t hwrng_attr_current_store(struct device *dev,
 	err = -ENODEV;
 	list_for_each_entry(rng, &rng_list, list) {
 		if (strcmp(rng->name, buf) == 0) {
-			if (rng == current_rng) {
-				err = 0;
-				break;
-			}
-			err = hwrng_init(rng);
-			if (err)
-				break;
-			hwrng_cleanup(current_rng);
-			current_rng = rng;
 			err = 0;
+			if (rng != current_rng)
+				err = set_current_rng(rng);
 			break;
 		}
 	}
@@ -261,17 +335,15 @@ static ssize_t hwrng_attr_current_show(struct device *dev,
 				       struct device_attribute *attr,
 				       char *buf)
 {
-	int err;
 	ssize_t ret;
-	const char *name = "none";
+	struct hwrng *rng;
 
-	err = mutex_lock_interruptible(&rng_mutex);
-	if (err)
-		return -ERESTARTSYS;
-	if (current_rng)
-		name = current_rng->name;
-	ret = snprintf(buf, PAGE_SIZE, "%s\n", name);
-	mutex_unlock(&rng_mutex);
+	rng = get_current_rng();
+	if (IS_ERR(rng))
+		return PTR_ERR(rng);
+
+	ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
+	put_rng(rng);
 
 	return ret;
 }
@@ -305,14 +377,14 @@ static DEVICE_ATTR(rng_available, S_IRUGO,
 		   NULL);
 
 
-static void unregister_miscdev(void)
+static void __exit unregister_miscdev(void)
 {
 	device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
 	device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 	misc_deregister(&rng_miscdev);
 }
 
-static int register_miscdev(void)
+static int __init register_miscdev(void)
 {
 	int err;
 
@@ -342,15 +414,22 @@ static int hwrng_fillfn(void *unused)
 	long rc;
 
 	while (!kthread_should_stop()) {
-		if (!current_rng)
+		struct hwrng *rng;
+
+		rng = get_current_rng();
+		if (IS_ERR(rng) || !rng)
 			break;
-		rc = rng_get_data(current_rng, rng_fillbuf,
+		mutex_lock(&reading_mutex);
+		rc = rng_get_data(rng, rng_fillbuf,
 				  rng_buffer_size(), 1);
+		mutex_unlock(&reading_mutex);
+		put_rng(rng);
 		if (rc <= 0) {
 			pr_warn("hwrng: no data available\n");
 			msleep_interruptible(10000);
 			continue;
 		}
+		/* Outside lock, sure, but y'know: randomness. */
 		add_hwgenerator_randomness((void *)rng_fillbuf, rc,
 					   rc * current_quality * 8 >> 10);
 	}
@@ -400,23 +479,16 @@ int hwrng_register(struct hwrng *rng)
 			goto out_unlock;
 	}
 
+	init_completion(&rng->cleanup_done);
+	complete(&rng->cleanup_done);
+
 	old_rng = current_rng;
-	if (!old_rng) {
-		err = hwrng_init(rng);
-		if (err)
-			goto out_unlock;
-		current_rng = rng;
-	}
 	err = 0;
 	if (!old_rng) {
-		err = register_miscdev();
-		if (err) {
-			hwrng_cleanup(rng);
-			current_rng = NULL;
+		err = set_current_rng(rng);
+		if (err)
 			goto out_unlock;
-		}
 	}
-	INIT_LIST_HEAD(&rng->list);
 	list_add_tail(&rng->list, &rng_list);
 
 	if (old_rng && !rng->init) {
@@ -439,42 +511,49 @@ EXPORT_SYMBOL_GPL(hwrng_register);
 
 void hwrng_unregister(struct hwrng *rng)
 {
-	int err;
-
 	mutex_lock(&rng_mutex);
 
 	list_del(&rng->list);
 	if (current_rng == rng) {
-		hwrng_cleanup(rng);
-		if (list_empty(&rng_list)) {
-			current_rng = NULL;
-		} else {
-			current_rng = list_entry(rng_list.prev, struct hwrng, list);
-			err = hwrng_init(current_rng);
-			if (err)
-				current_rng = NULL;
+		drop_current_rng();
+		if (!list_empty(&rng_list)) {
+			struct hwrng *tail;
+
+			tail = list_entry(rng_list.prev, struct hwrng, list);
+
+			set_current_rng(tail);
 		}
 	}
+
 	if (list_empty(&rng_list)) {
-		unregister_miscdev();
+		mutex_unlock(&rng_mutex);
 		if (hwrng_fill)
 			kthread_stop(hwrng_fill);
-	}
+	} else
+		mutex_unlock(&rng_mutex);
 
-	mutex_unlock(&rng_mutex);
+	wait_for_completion(&rng->cleanup_done);
 }
 EXPORT_SYMBOL_GPL(hwrng_unregister);
 
-static void __exit hwrng_exit(void)
+static int __init hwrng_modinit(void)
+{
+	return register_miscdev();
+}
+
+static void __exit hwrng_modexit(void)
 {
 	mutex_lock(&rng_mutex);
 	BUG_ON(current_rng);
 	kfree(rng_buffer);
 	kfree(rng_fillbuf);
 	mutex_unlock(&rng_mutex);
+
+	unregister_miscdev();
 }
 
-module_exit(hwrng_exit);
+module_init(hwrng_modinit);
+module_exit(hwrng_modexit);
 
 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 MODULE_LICENSE("GPL");