random: convert to using fops->write_iter()

Now that the read side has been converted to fix a regression with
splice, convert the write side as well to have some symmetry in the
interface used (and help deprecate ->write()).

Signed-off-by: Jens Axboe <axboe@kernel.dk>
[Jason: cleaned up random_ioctl a bit, require full writes in
 RNDADDENTROPY since it's crediting entropy, simplify control flow of
 write_pool(), and incorporate suggestions from Al.]
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

drivers/char/random.c

@@ -1274,39 +1274,31 @@ static __poll_t random_poll(struct file *file, poll_table *wait)
 	return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
 }
 
-static int write_pool(const char __user *ubuf, size_t len)
+static ssize_t write_pool(struct iov_iter *iter)
 {
-	size_t block_len;
-	int ret = 0;
 	u8 block[BLAKE2S_BLOCK_SIZE];
+	ssize_t ret = 0;
+	size_t copied;
 
-	while (len) {
-		block_len = min(len, sizeof(block));
-		if (copy_from_user(block, ubuf, block_len)) {
-			ret = -EFAULT;
-			goto out;
-		}
-		len -= block_len;
-		ubuf += block_len;
-		mix_pool_bytes(block, block_len);
+	if (unlikely(!iov_iter_count(iter)))
+		return 0;
+
+	for (;;) {
+		copied = copy_from_iter(block, sizeof(block), iter);
+		ret += copied;
+		mix_pool_bytes(block, copied);
+		if (!iov_iter_count(iter) || copied != sizeof(block))
+			break;
 		cond_resched();
 	}
 
-out:
 	memzero_explicit(block, sizeof(block));
-	return ret;
+	return ret ? ret : -EFAULT;
 }
 
-static ssize_t random_write(struct file *file, const char __user *ubuf,
-			    size_t len, loff_t *ppos)
+static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
 {
-	int ret;
-
-	ret = write_pool(ubuf, len);
-	if (ret)
-		return ret;
-
-	return (ssize_t)len;
+	return write_pool(iter);
 }
 
 static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
@@ -1345,9 +1337,8 @@ static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
 
 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 {
-	int size, ent_count;
 	int __user *p = (int __user *)arg;
-	int retval;
+	int ent_count;
 
 	switch (cmd) {
 	case RNDGETENTCNT:
@@ -1364,20 +1355,32 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 			return -EINVAL;
 		credit_init_bits(ent_count);
 		return 0;
-	case RNDADDENTROPY:
+	case RNDADDENTROPY: {
+		struct iov_iter iter;
+		struct iovec iov;
+		ssize_t ret;
+		int len;
+
 		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++))
+		if (get_user(len, p++))
+			return -EFAULT;
+		ret = import_single_range(WRITE, p, len, &iov, &iter);
+		if (unlikely(ret))
+			return ret;
+		ret = write_pool(&iter);
+		if (unlikely(ret < 0))
+			return ret;
+		/* Since we're crediting, enforce that it was all written into the pool. */
+		if (unlikely(ret != len))
 			return -EFAULT;
-		retval = write_pool((const char __user *)p, size);
-		if (retval < 0)
-			return retval;
 		credit_init_bits(ent_count);
 		return 0;
+	}
 	case RNDZAPENTCNT:
 	case RNDCLEARPOOL:
 		/* No longer has any effect. */
@@ -1403,7 +1406,7 @@ static int random_fasync(int fd, struct file *filp, int on)
 
 const struct file_operations random_fops = {
 	.read_iter = random_read_iter,
-	.write = random_write,
+	.write_iter = random_write_iter,
 	.poll = random_poll,
 	.unlocked_ioctl = random_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,
@@ -1413,7 +1416,7 @@ const struct file_operations random_fops = {
 
 const struct file_operations urandom_fops = {
 	.read_iter = urandom_read_iter,
-	.write = random_write,
+	.write_iter = random_write_iter,
 	.unlocked_ioctl = random_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,
 	.fasync = random_fasync,