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    Subject[PATCH 4.14 033/237] random: make /dev/random be almost like /dev/urandom
    Date
    From: Andy Lutomirski <luto@kernel.org>

    commit 30c08efec8884fb106b8e57094baa51bb4c44e32 upstream.

    This patch changes the read semantics of /dev/random to be the same
    as /dev/urandom except that reads will block until the CRNG is
    ready.

    None of the cleanups that this enables have been done yet. As a
    result, this gives a warning about an unused function.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Link: https://lore.kernel.org/r/5e6ac8831c6cf2e56a7a4b39616d1732b2bdd06c.1577088521.git.luto@kernel.org
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 54 ++++++++++++--------------------------------------
    1 file changed, 13 insertions(+), 41 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -354,7 +354,6 @@
    #define INPUT_POOL_WORDS (1 << (INPUT_POOL_SHIFT-5))
    #define OUTPUT_POOL_SHIFT 10
    #define OUTPUT_POOL_WORDS (1 << (OUTPUT_POOL_SHIFT-5))
    -#define SEC_XFER_SIZE 512
    #define EXTRACT_SIZE 10


    @@ -804,7 +803,6 @@ retry:
    if (entropy_bits >= random_read_wakeup_bits &&
    wq_has_sleeper(&random_read_wait)) {
    wake_up_interruptible(&random_read_wait);
    - kill_fasync(&fasync, SIGIO, POLL_IN);
    }
    /* If the input pool is getting full, and the blocking
    * pool has room, send some entropy to the blocking
    @@ -1925,43 +1923,6 @@ void rand_initialize_disk(struct gendisk
    #endif

    static ssize_t
    -_random_read(int nonblock, char __user *buf, size_t nbytes)
    -{
    - ssize_t n;
    -
    - if (nbytes == 0)
    - return 0;
    -
    - nbytes = min_t(size_t, nbytes, SEC_XFER_SIZE);
    - while (1) {
    - n = extract_entropy_user(&blocking_pool, buf, nbytes);
    - if (n < 0)
    - return n;
    - trace_random_read(n*8, (nbytes-n)*8,
    - ENTROPY_BITS(&blocking_pool),
    - ENTROPY_BITS(&input_pool));
    - if (n > 0)
    - return n;
    -
    - /* Pool is (near) empty. Maybe wait and retry. */
    - if (nonblock)
    - return -EAGAIN;
    -
    - wait_event_interruptible(random_read_wait,
    - blocking_pool.initialized &&
    - (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits));
    - if (signal_pending(current))
    - return -ERESTARTSYS;
    - }
    -}
    -
    -static ssize_t
    -random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
    -{
    - return _random_read(file->f_flags & O_NONBLOCK, buf, nbytes);
    -}
    -
    -static ssize_t
    urandom_read_nowarn(struct file *file, char __user *buf, size_t nbytes,
    loff_t *ppos)
    {
    @@ -1993,15 +1954,26 @@ urandom_read(struct file *file, char __u
    return urandom_read_nowarn(file, buf, nbytes, ppos);
    }

    +static ssize_t
    +random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
    +{
    + int ret;
    +
    + ret = wait_for_random_bytes();
    + if (ret != 0)
    + return ret;
    + return urandom_read_nowarn(file, buf, nbytes, ppos);
    +}
    +
    static unsigned int
    random_poll(struct file *file, poll_table * wait)
    {
    unsigned int mask;

    - poll_wait(file, &random_read_wait, wait);
    + poll_wait(file, &crng_init_wait, wait);
    poll_wait(file, &random_write_wait, wait);
    mask = 0;
    - if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits)
    + if (crng_ready())
    mask |= POLLIN | POLLRDNORM;
    if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits)
    mask |= POLLOUT | POLLWRNORM;

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