linux-kernel - [PATCH] random: convert to using fops->write

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Date:   Thu, 19 May 2022 17:43:15 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] 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@...nel.dk>

---

Jason, this has only been booted. I did verify that it seems to take a
write just fine, but I would appreciate if you could vet this one with
your testing. Thanks!

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 41ca5966aa4f..3da04068c225 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1283,20 +1283,20 @@ 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 size_t write_pool(struct iov_iter *iter)
 {
 	size_t block_len;
 	int ret = 0;
 	u8 block[BLAKE2S_BLOCK_SIZE];
 
-	while (len) {
-		block_len = min(len, sizeof(block));
-		if (copy_from_user(block, ubuf, block_len)) {
-			ret = -EFAULT;
+	while (iov_iter_count(iter)) {
+		block_len = min(iov_iter_count(iter), sizeof(block));
+		if (!copy_from_iter(block, block_len, iter)) {
+			if (!ret)
+				ret = -EFAULT;
 			goto out;
 		}
-		len -= block_len;
-		ubuf += block_len;
+		ret += block_len;
 		mix_pool_bytes(block, block_len);
 		cond_resched();
 	}
@@ -1306,16 +1306,9 @@ static int write_pool(const char __user *ubuf, size_t len)
 	return ret;
 }
 
-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 *from)
 {
-	int ret;
-
-	ret = write_pool(ubuf, len);
-	if (ret)
-		return ret;
-
-	return (ssize_t)len;
+	return write_pool(from);
 }
 
 static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *to)
@@ -1373,7 +1366,10 @@ 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;
+
 		if (!capable(CAP_SYS_ADMIN))
 			return -EPERM;
 		if (get_user(ent_count, p++))
@@ -1382,11 +1378,16 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 			return -EINVAL;
 		if (get_user(size, p++))
 			return -EFAULT;
-		retval = write_pool((const char __user *)p, size);
+
+		iov.iov_base = p;
+		iov.iov_len = size;
+		iov_iter_init(&iter, WRITE, &iov, 1, size);
+		retval = write_pool(&iter);
 		if (retval < 0)
 			return retval;
 		credit_init_bits(ent_count);
 		return 0;
+		}
 	case RNDZAPENTCNT:
 	case RNDCLEARPOOL:
 		/* No longer has any effect. */
@@ -1412,7 +1413,7 @@ 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,
@@ -1423,7 +1424,7 @@ 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,

-- 
Jens Axboe