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

Jens Axboe
2022-05-19T23:31:54Z

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 | 44 ++++++++++++++++++++++---------------------
1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0958fa91a964..d000fe6fbb5a 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -397,11 +397,12 @@ void get_random_bytes(void *buf, size_t len)
}
EXPORT_SYMBOL(get_random_bytes);

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

if (!len)
return 0;
@@ -418,25 +419,23 @@ static ssize_t get_random_bytes_user(void __user *ubuf, size_t len)
* the user directly.
*/
if (len <= CHACHA_KEY_SIZE) {
- ret = len - copy_to_user(ubuf, &chacha_state[4], len);
+ ret = copy_to_iter(&chacha_state[4], len, to);
goto out_zero_chacha;
}

for (;;) {
+ size_t copied;
+
chacha20_block(chacha_state, output);
if (unlikely(chacha_state[12] == 0))
++chacha_state[13];

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

@@ -1248,6 +1247,9 @@ static void __cold try_to_generate_entropy(void)

SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
{
+ struct iovec iov = { .iov_base = ubuf };
+ struct iov_iter iter;
+
if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
return -EINVAL;

@@ -1270,7 +1272,9 @@ SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags
if (unlikely(ret))
return ret;
}
- return get_random_bytes_user(ubuf, len);
+ iov.iov_len = len;
+ iov_iter_init(&iter, READ, &iov, 1, len);
+ return get_random_bytes_user(&iter);
}

static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1314,8 +1318,7 @@ static ssize_t random_write(struct file *file, const char __user *ubuf,
return (ssize_t)len;
}

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

@@ -1332,22 +1335,21 @@ static ssize_t urandom_read(struct file *file, char __user *ubuf,
else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
--maxwarn;
pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
- current->comm, len);
+ current->comm, iov_iter_count(to));
}
}

- return get_random_bytes_user(ubuf, len);
+ return get_random_bytes_user(to);
}

-static ssize_t random_read(struct file *file, char __user *ubuf,
- size_t len, 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(ubuf, len);
+ return get_random_bytes_user(to);
}

static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
@@ -1409,7 +1411,7 @@ 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,
@@ -1419,7 +1421,7 @@ 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