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Subject[PATCH 4.19 022/234] 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
@@ -1988,43 +1986,6 @@ 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)
{
@@ -2056,15 +2017,26 @@ 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;

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