[PATCH v4 1/3] random: convert to using fops->read_iter()

Jason A. Donenfeld
2022-05-20T09:45:29Z

From: Jens Axboe <axboe@kernel.dk>

This is a pre-requisite to wiring up splice() again for the random
and urandom drivers. It also allows us to remove the INT_MAX check in
getrandom(), because import_single_range() applies capping internally.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
[Jason: rewrote get_random_bytes_user() to simplify and also incorporate
additional suggestions from Al.]
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
drivers/char/random.c | 55 +++++++++++++++++++------------------------
1 file changed, 24 insertions(+), 31 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0958fa91a964..f8cd747acec2 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -397,13 +397,13 @@ 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;
u32 chacha_state[CHACHA_STATE_WORDS];
u8 output[CHACHA_BLOCK_SIZE];
+ size_t ret = 0, copied;

- if (!len)
+ if (!iov_iter_count(to))
return 0;

/*
@@ -417,8 +417,8 @@ static ssize_t get_random_bytes_user(void __user *ubuf, size_t len)
* use chacha_state after, so we can simply return those bytes to
* the user directly.
*/
- if (len <= CHACHA_KEY_SIZE) {
- ret = len - copy_to_user(ubuf, &chacha_state[4], len);
+ if (iov_iter_count(to) <= CHACHA_KEY_SIZE) {
+ ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, to);
goto out_zero_chacha;
}

@@ -427,17 +427,9 @@ static ssize_t get_random_bytes_user(void __user *ubuf, size_t len)
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;
- break;
- }
-
- ubuf += block_len;
- ret += block_len;
- len -= block_len;
- if (!len)
+ copied = copy_to_iter(output, CHACHA_BLOCK_SIZE, to);
+ ret += copied;
+ if (!iov_iter_count(to) || copied != CHACHA_BLOCK_SIZE)
break;

BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0);
@@ -1248,6 +1240,10 @@ static void __cold try_to_generate_entropy(void)

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

@@ -1258,19 +1254,18 @@ SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags
if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
return -EINVAL;

- if (len > INT_MAX)
- len = INT_MAX;
-
if (!crng_ready() && !(flags & GRND_INSECURE)) {
- int ret;
-
if (flags & GRND_NONBLOCK)
return -EAGAIN;
ret = wait_for_random_bytes();
if (unlikely(ret))
return ret;
}
- return get_random_bytes_user(ubuf, len);
+
+ ret = import_single_range(READ, ubuf, len, &iov, &to);
+ if (unlikely(ret))
+ return ret;
+ return get_random_bytes_user(&to);
}

static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1314,8 +1309,7 @@ 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 +1326,21 @@ 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 +1402,7 @@ 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 +1412,7 @@ 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