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SubjectRe: [PATCH] random: convert to using fops->write_iter()
On Thu, May 19, 2022 at 05:43:15PM -0600, Jens Axboe wrote:

> -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;
>
> - 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;
> }

Feed it a buffer with only 1 byte mapped, watch it'll pass to mix_pool_bytes().
And see how much of 'block' has been used uninitialized...

And why bother with that min thing, anyway?

ssize_t ret = 0;

while (iov_iter_count(iter)) {
u8 block[BLAKE2S_BLOCK_SIZE];
size_t copied = copy_from_iter(block, sizeof(block), iter);
if (!copied) {
if (!ret)
ret = -EFAULT;
break;
}
mix_pool_bytes(block, copied);
ret += copied;
}
return ret;

and be done with that...

> @@ -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);

That'd be
import_single_range(WRITE, p, size, &iov, &iter);

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