[PATCH 5.17 106/111] random: convert to using fops->read_iter()

Greg Kroah-Hartman
2022-05-27T12:02:53Z

From: Jens Axboe <axboe@kernel.dk>

commit 1b388e7765f2eaa137cf5d92b47ef5925ad83ced upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 66 ++++++++++++++++++++++----------------------------
1 file changed, 30 insertions(+), 36 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -52,6 +52,7 @@
#include <linux/uuid.h>
#include <linux/uaccess.h>
#include <linux/siphash.h>
+#include <linux/uio.h>
#include <crypto/chacha.h>
#include <crypto/blake2s.h>
#include <asm/processor.h>
@@ -446,13 +447,13 @@ void get_random_bytes(void *buf, size_t
}
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 *iter)
{
- size_t block_len, left, ret = 0;
u32 chacha_state[CHACHA_STATE_WORDS];
- u8 output[CHACHA_BLOCK_SIZE];
+ u8 block[CHACHA_BLOCK_SIZE];
+ size_t ret = 0, copied;

- if (!len)
+ if (unlikely(!iov_iter_count(iter)))
return 0;

/*
@@ -466,30 +467,22 @@ static ssize_t get_random_bytes_user(voi
* 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(iter) <= CHACHA_KEY_SIZE) {
+ ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, iter);
goto out_zero_chacha;
}

for (;;) {
- chacha20_block(chacha_state, output);
+ chacha20_block(chacha_state, block);
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(block, sizeof(block), iter);
+ ret += copied;
+ if (!iov_iter_count(iter) || copied != sizeof(block))
break;

- BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0);
+ BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
if (ret % PAGE_SIZE == 0) {
if (signal_pending(current))
break;
@@ -497,7 +490,7 @@ static ssize_t get_random_bytes_user(voi
}
}

- memzero_explicit(output, sizeof(output));
+ memzero_explicit(block, sizeof(block));
out_zero_chacha:
memzero_explicit(chacha_state, sizeof(chacha_state));
return ret ? ret : -EFAULT;
@@ -1226,6 +1219,10 @@ static void __cold try_to_generate_entro

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

@@ -1236,19 +1233,18 @@ SYSCALL_DEFINE3(getrandom, char __user *
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, &iter);
+ if (unlikely(ret))
+ return ret;
+ return get_random_bytes_user(&iter);
}

static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1292,8 +1288,7 @@ static ssize_t random_write(struct file
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 *iter)
{
static int maxwarn = 10;

@@ -1302,23 +1297,22 @@ static ssize_t urandom_read(struct file
++urandom_warning.missed;
else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
--maxwarn;
- pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
- current->comm, len);
+ pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
+ current->comm, iov_iter_count(iter));
}
}

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

-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 *iter)
{
int ret;

ret = wait_for_random_bytes();
if (ret != 0)
return ret;
- return get_random_bytes_user(ubuf, len);
+ return get_random_bytes_user(iter);
}

static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
@@ -1380,7 +1374,7 @@ static int random_fasync(int fd, struct
}

const struct file_operations random_fops = {
- .read = random_read,
+ .read_iter = random_read_iter,
.write = random_write,
.poll = random_poll,
.unlocked_ioctl = random_ioctl,
@@ -1390,7 +1384,7 @@ 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,