[PATCH 1/2] random: convert to using fops->read_iter()

Jens Axboe
2022-05-19T19:31:45Z

This is a pre-requisite to writing up splice() again for the random
and urandom drivers.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
drivers/char/random.c | 37 +++++++++++++++++++------------------
1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 4c9adb4f3d5d..529afd31d549 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -528,11 +528,12 @@ void get_random_bytes(void *buf, size_t nbytes)
}
EXPORT_SYMBOL(get_random_bytes);

-static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
+static ssize_t get_random_bytes_user(struct iov_iter *to)
{
- size_t len, left, ret = 0;
+ size_t len, ret = 0;
u32 chacha_state[CHACHA_STATE_WORDS];
u8 output[CHACHA_BLOCK_SIZE];
+ size_t nbytes = iov_iter_count(to);

if (!nbytes)
return 0;
@@ -549,7 +550,7 @@ static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
* the user directly.
*/
if (nbytes <= CHACHA_KEY_SIZE) {
- ret = nbytes - copy_to_user(buf, &chacha_state[4], nbytes);
+ ret = copy_to_iter(&chacha_state[4], nbytes, to);
goto out_zero_chacha;
}

@@ -559,13 +560,10 @@ static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
++chacha_state[13];

len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE);
- left = copy_to_user(buf, output, len);
- if (left) {
- ret += len - left;
+ len = copy_to_iter(output, len, to);
+ if (!len)
break;
- }

- buf += len;
ret += len;
nbytes -= len;
if (!nbytes)
@@ -1466,6 +1464,9 @@ static void try_to_generate_entropy(void)
SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
flags)
{
+ struct iovec iov = { .iov_base = buf };
+ struct iov_iter iter;
+
if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
return -EINVAL;

@@ -1488,7 +1489,9 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
if (unlikely(ret))
return ret;
}
- return get_random_bytes_user(buf, count);
+ iov.iov_len = count;
+ iov_iter_init(&iter, READ, &iov, 1, count);
+ return get_random_bytes_user(&iter);
}

static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1540,8 +1543,7 @@ static ssize_t random_write(struct file *file, const char __user *buffer,
return (ssize_t)count;
}

-static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
- loff_t *ppos)
+static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *to)
{
static int maxwarn = 10;

@@ -1556,21 +1558,20 @@ static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
maxwarn--;
if (__ratelimit(&urandom_warning))
pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
- current->comm, nbytes);
+ current->comm, iov_iter_count(to));
}

- return get_random_bytes_user(buf, nbytes);
+ return get_random_bytes_user(to);
}

-static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
- loff_t *ppos)
+static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *to)
{
int ret;

ret = wait_for_random_bytes();
if (ret != 0)
return ret;
- return get_random_bytes_user(buf, nbytes);
+ return get_random_bytes_user(to);
}

static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
@@ -1639,7 +1640,7 @@ static int random_fasync(int fd, struct file *filp, int on)
}

const struct file_operations random_fops = {
- .read = random_read,
+ .read_iter = random_read_iter,
.write = random_write,
.poll = random_poll,
.unlocked_ioctl = random_ioctl,
@@ -1649,7 +1650,7 @@ const struct file_operations random_fops = {
};

const struct file_operations urandom_fops = {
- .read = urandom_read,
+ .read_iter = urandom_read_iter,
.write = random_write,
.unlocked_ioctl = random_ioctl,
.compat_ioctl = compat_ptr_ioctl,
--
2.35.1