Commit 30c08efe authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Theodore Ts'o
Browse files

random: make /dev/random be almost like /dev/urandom 



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: default avatarAndy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/5e6ac8831c6cf2e56a7a4b39616d1732b2bdd06c.1577088521.git.luto@kernel.org


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 48446f19

drivers/char/random.c

+14 −41
Original line number Diff line number Diff line
@@ -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
@@ -803,7 +802,6 @@ 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
@@ -1031,6 +1029,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r) 
		crng_init = 2;

		process_random_ready_list();

		wake_up_interruptible(&crng_init_wait);

		kill_fasync(&fasync, SIGIO, POLL_IN);

		pr_notice("random: crng init done\n");

		if (unseeded_warning.missed) {

			pr_notice("random: %d get_random_xx warning(s) missed "
@@ -1982,43 +1981,6 @@ void rand_initialize_disk(struct gendisk *disk) 
}

#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)
@@ -2051,15 +2013,26 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) 
	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 __poll_t

random_poll(struct file *file, poll_table * wait)

{

	__poll_t 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 |= EPOLLIN | EPOLLRDNORM;

	if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits)

		mask |= EPOLLOUT | EPOLLWRNORM;

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