linux-kernel - [PATCH 5.4 013/240] random: make /dev/random be almost like /dev/urandom

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Date:   Mon, 20 Jun 2022 14:48:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Theodore Tso <tytso@....edu>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 5.4 013/240] random: make /dev/random be almost like /dev/urandom

From: Andy Lutomirski <luto@...nel.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@...nel.org>
Link: https://lore.kernel.org/r/5e6ac8831c6cf2e56a7a4b39616d1732b2bdd06c.1577088521.git.luto@kernel.org
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -2006,43 +2004,6 @@ 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)
 {
@@ -2074,15 +2035,26 @@ 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 __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;