random.c

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	xfer_secondary_pool(r, nbytes);
	nbytes = account(r, nbytes, 0, 0);

	while (nbytes) {
		if (need_resched()) {
			if (signal_pending(current)) {
				if (ret == 0)
					ret = -ERESTARTSYS;
				break;
			}
			schedule();
		}

		extract_buf(r, tmp);
		i = min_t(int, nbytes, EXTRACT_SIZE);
		if (copy_to_user(buf, tmp, i)) {
			ret = -EFAULT;
			break;
		}

		nbytes -= i;
		buf += i;
		ret += i;
	}

	/* Wipe data just returned from memory */
	memset(tmp, 0, sizeof(tmp));

	return ret;
}

/*
 * This function is the exported kernel interface.  It returns some
 * number of good random numbers, suitable for seeding TCP sequence
 * numbers, etc.
 */
void get_random_bytes(void *buf, int nbytes)
{
	extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
}

EXPORT_SYMBOL(get_random_bytes);

/*
 * init_std_data - initialize pool with system data
 *
 * @r: pool to initialize
 *
 * This function clears the pool's entropy count and mixes some system
 * data into the pool to prepare it for use. The pool is not cleared
 * as that can only decrease the entropy in the pool.
 */
static void init_std_data(struct entropy_store *r)
{
	ktime_t now;
	unsigned long flags;

	spin_lock_irqsave(&r->lock, flags);
	r->entropy_count = 0;
	spin_unlock_irqrestore(&r->lock, flags);

	now = ktime_get_real();
	add_entropy_words(r, (__u32 *)&now, sizeof(now)/4);
	add_entropy_words(r, (__u32 *)utsname(),
			  sizeof(*(utsname()))/4);
}

static int __init rand_initialize(void)
{
	init_std_data(&input_pool);
	init_std_data(&blocking_pool);
	init_std_data(&nonblocking_pool);
	return 0;
}
module_init(rand_initialize);

void rand_initialize_irq(int irq)
{
	struct timer_rand_state *state;

	if (irq >= NR_IRQS || irq_timer_state[irq])
		return;

	/*
	 * If kzalloc returns null, we just won't use that entropy
	 * source.
	 */
	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
	if (state)
		irq_timer_state[irq] = state;
}

#ifdef CONFIG_BLOCK
void rand_initialize_disk(struct gendisk *disk)
{
	struct timer_rand_state *state;

	/*
	 * If kzalloc returns null, we just won't use that entropy
	 * source.
	 */
	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
	if (state)
		disk->random = state;
}
#endif

static ssize_t
random_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
{
	ssize_t n, retval = 0, count = 0;

	if (nbytes == 0)
		return 0;

	while (nbytes > 0) {
		n = nbytes;
		if (n > SEC_XFER_SIZE)
			n = SEC_XFER_SIZE;

		DEBUG_ENT("reading %d bits\n", n*8);

		n = extract_entropy_user(&blocking_pool, buf, n);

		DEBUG_ENT("read got %d bits (%d still needed)\n",
			  n*8, (nbytes-n)*8);

		if (n == 0) {
			if (file->f_flags & O_NONBLOCK) {
				retval = -EAGAIN;
				break;
			}

			DEBUG_ENT("sleeping?\n");

			wait_event_interruptible(random_read_wait,
				input_pool.entropy_count >=
						 random_read_wakeup_thresh);

			DEBUG_ENT("awake\n");

			if (signal_pending(current)) {
				retval = -ERESTARTSYS;
				break;
			}

			continue;
		}

		if (n < 0) {
			retval = n;
			break;
		}
		count += n;
		buf += n;
		nbytes -= n;
		break;		/* This break makes the device work */
				/* like a named pipe */
	}

	/*
	 * If we gave the user some bytes, update the access time.
	 */
	if (count)
		file_accessed(file);

	return (count ? count : retval);
}

static ssize_t
urandom_read(struct file * file, char __user * buf,
		      size_t nbytes, loff_t *ppos)
{
	return extract_entropy_user(&nonblocking_pool, buf, nbytes);
}

static unsigned int
random_poll(struct file *file, poll_table * wait)
{
	unsigned int mask;

	poll_wait(file, &random_read_wait, wait);
	poll_wait(file, &random_write_wait, wait);
	mask = 0;
	if (input_pool.entropy_count >= random_read_wakeup_thresh)
		mask |= POLLIN | POLLRDNORM;
	if (input_pool.entropy_count < random_write_wakeup_thresh)
		mask |= POLLOUT | POLLWRNORM;
	return mask;
}

static int
write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
{
	size_t bytes;
	__u32 buf[16];
	const char __user *p = buffer;

	while (count > 0) {
		bytes = min(count, sizeof(buf));
		if (copy_from_user(&buf, p, bytes))
			return -EFAULT;

		count -= bytes;
		p += bytes;

		add_entropy_words(r, buf, (bytes + 3) / 4);
	}

	return 0;
}

static ssize_t
random_write(struct file * file, const char __user * buffer,
	     size_t count, loff_t *ppos)
{
	size_t ret;
	struct inode *inode = file->f_path.dentry->d_inode;

	ret = write_pool(&blocking_pool, buffer, count);
	if (ret)
		return ret;
	ret = write_pool(&nonblocking_pool, buffer, count);
	if (ret)
		return ret;

	inode->i_mtime = current_fs_time(inode->i_sb);
	mark_inode_dirty(inode);
	return (ssize_t)count;
}

static int
random_ioctl(struct inode * inode, struct file * file,
	     unsigned int cmd, unsigned long arg)
{
	int size, ent_count;
	int __user *p = (int __user *)arg;
	int retval;

	switch (cmd) {
	case RNDGETENTCNT:
		ent_count = input_pool.entropy_count;
		if (put_user(ent_count, p))
			return -EFAULT;
		return 0;
	case RNDADDTOENTCNT:
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		if (get_user(ent_count, p))
			return -EFAULT;
		credit_entropy_store(&input_pool, ent_count);
		/*
		 * Wake up waiting processes if we have enough
		 * entropy.
		 */
		if (input_pool.entropy_count >= random_read_wakeup_thresh)
			wake_up_interruptible(&random_read_wait);
		return 0;
	case RNDADDENTROPY:
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		if (get_user(ent_count, p++))
			return -EFAULT;
		if (ent_count < 0)
			return -EINVAL;
		if (get_user(size, p++))
			return -EFAULT;
		retval = write_pool(&input_pool, (const char __user *)p,
				    size);
		if (retval < 0)
			return retval;
		credit_entropy_store(&input_pool, ent_count);
		/*
		 * Wake up waiting processes if we have enough
		 * entropy.
		 */
		if (input_pool.entropy_count >= random_read_wakeup_thresh)
			wake_up_interruptible(&random_read_wait);
		return 0;
	case RNDZAPENTCNT:
	case RNDCLEARPOOL:
		/* Clear the entropy pool counters. */
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		init_std_data(&input_pool);
		init_std_data(&blocking_pool);
		init_std_data(&nonblocking_pool);
		return 0;
	default:
		return -EINVAL;
	}
}

const struct file_operations random_fops = {
	.read  = random_read,
	.write = random_write,
	.poll  = random_poll,
	.ioctl = random_ioctl,
};

const struct file_operations urandom_fops = {
	.read  = urandom_read,
	.write = random_write,
	.ioctl = random_ioctl,
};

/***************************************************************
 * Random UUID interface
 *
 * Used here for a Boot ID, but can be useful for other kernel
 * drivers.
 ***************************************************************/

/*
 * Generate random UUID
 */
void generate_random_uuid(unsigned char uuid_out[16])
{
	get_random_bytes(uuid_out, 16);
	/* Set UUID version to 4 --- truely random generation */
	uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
	/* Set the UUID variant to DCE */
	uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
}

EXPORT_SYMBOL(generate_random_uuid);

/********************************************************************
 *
 * Sysctl interface
 *
 ********************************************************************/

#ifdef CONFIG_SYSCTL

#include <linux/sysctl.h>

static int min_read_thresh = 8, min_write_thresh;
static int max_read_thresh = INPUT_POOL_WORDS * 32;
static int max_write_thresh = INPUT_POOL_WORDS * 32;
static char sysctl_bootid[16];

/*
 * These functions is used to return both the bootid UUID, and random
 * UUID.  The difference is in whether table->data is NULL; if it is,
 * then a new UUID is generated and returned to the user.
 *
 * If the user accesses this via the proc interface, it will be returned
 * as an ASCII string in the standard UUID format.  If accesses via the
 * sysctl system call, it is returned as 16 bytes of binary data.
 */
static int proc_do_uuid(ctl_table *table, int write, struct file *filp,
			void __user *buffer, size_t *lenp, loff_t *ppos)
{
	ctl_table fake_table;
	unsigned char buf[64], tmp_uuid[16], *uuid;

	uuid = table->data;
	if (!uuid) {
		uuid = tmp_uuid;
		uuid[8] = 0;
	}
	if (uuid[8] == 0)
		generate_random_uuid(uuid);

	sprintf(buf, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-"
		"%02x%02x%02x%02x%02x%02x",
		uuid[0],  uuid[1],  uuid[2],  uuid[3],
		uuid[4],  uuid[5],  uuid[6],  uuid[7],
		uuid[8],  uuid[9],  uuid[10], uuid[11],
		uuid[12], uuid[13], uuid[14], uuid[15]);
	fake_table.data = buf;
	fake_table.maxlen = sizeof(buf);

	return proc_dostring(&fake_table, write, filp, buffer, lenp, ppos);
}

static int uuid_strategy(ctl_table *table, int __user *name, int nlen,
			 void __user *oldval, size_t __user *oldlenp,
			 void __user *newval, size_t newlen)
{
	unsigned char tmp_uuid[16], *uuid;
	unsigned int len;

	if (!oldval || !oldlenp)
		return 1;

	uuid = table->data;
	if (!uuid) {
		uuid = tmp_uuid;
		uuid[8] = 0;
	}
	if (uuid[8] == 0)
		generate_random_uuid(uuid);

	if (get_user(len, oldlenp))
		return -EFAULT;
	if (len) {
		if (len > 16)
			len = 16;
		if (copy_to_user(oldval, uuid, len) ||
		    put_user(len, oldlenp))
			return -EFAULT;
	}
	return 1;
}

static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
ctl_table random_table[] = {
	{
		.ctl_name 	= RANDOM_POOLSIZE,
		.procname	= "poolsize",
		.data		= &sysctl_poolsize,
		.maxlen		= sizeof(int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},
	{