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    Subject[PATCH 5.10 159/163] random: convert to using fops->read_iter()
    Date
    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>
    @@ -448,13 +449,13 @@ 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;

    /*
    @@ -468,30 +469,22 @@ 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;
    @@ -499,7 +492,7 @@ 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;
    @@ -1228,6 +1221,10 @@ 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;

    @@ -1238,19 +1235,18 @@ 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)
    @@ -1294,8 +1290,7 @@ 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;

    @@ -1304,23 +1299,22 @@ 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)
    @@ -1382,7 +1376,7 @@ 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,
    @@ -1392,7 +1386,7 @@ 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,

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