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Message-Id: <20220221154721.2292443-1-Jason@zx2c4.com>
Date: Mon, 21 Feb 2022 16:47:21 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: linux-kernel@...r.kernel.org
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
Theodore Ts'o <tytso@....edu>,
Eric Biggers <ebiggers@...nel.org>,
Eric Biggers <ebiggers@...gle.com>,
Dominik Brodowski <linux@...inikbrodowski.net>
Subject: [PATCH v4] random: always wake up entropy writers after extraction
Now that POOL_BITS == POOL_MIN_BITS, we must unconditionally wake up
entropy writers after every extraction. Therefore there's no point of
write_wakeup_threshold, so we can move it to the dustbin of unused
compatibility sysctls. While we're at it, we can fix a small comparison
where we were waking up after <= min rather than < min.
Cc: Theodore Ts'o <tytso@....edu>
Suggested-by: Eric Biggers <ebiggers@...nel.org>
Reviewed-by: Eric Biggers <ebiggers@...gle.com>
Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
v4 keeps the file writable to avoid breaking userspace and updates
kernel.rst.
Documentation/admin-guide/sysctl/kernel.rst | 7 +++--
drivers/char/random.c | 33 +++++++--------------
2 files changed, 16 insertions(+), 24 deletions(-)
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index d359bcfadd39..d3c6d9a501a9 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1029,14 +1029,17 @@ This is a directory, with the following entries:
* ``poolsize``: the entropy pool size, in bits;
* ``urandom_min_reseed_secs``: obsolete (used to determine the minimum
- number of seconds between urandom pool reseeding).
+ number of seconds between urandom pool reseeding). This file is
+ writable for compatibility purposes, but writing to it has no effect
+ on any RNG behavior.
* ``uuid``: a UUID generated every time this is retrieved (this can
thus be used to generate UUIDs at will);
* ``write_wakeup_threshold``: when the entropy count drops below this
(as a number of bits), processes waiting to write to ``/dev/random``
- are woken up.
+ are woken up. This file is writable for compatibility purposes, but
+ writing to it has no effect on any RNG behavior.
If ``drivers/char/random.c`` is built with ``ADD_INTERRUPT_BENCH``
defined, these additional entries are present:
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 20538e9b1a2c..3b30e764eeef 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -296,12 +296,6 @@ enum {
*/
static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
static struct fasync_struct *fasync;
-/*
- * If the entropy count falls under this number of bits, then we
- * should wake up processes which are selecting or polling on write
- * access to /dev/random.
- */
-static int random_write_wakeup_bits = POOL_MIN_BITS;
static DEFINE_SPINLOCK(random_ready_list_lock);
static LIST_HEAD(random_ready_list);
@@ -739,10 +733,8 @@ static void crng_reseed(struct crng_state *crng, bool use_input_pool)
return;
} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
extract_entropy(buf.key, sizeof(buf.key));
- if (random_write_wakeup_bits) {
- wake_up_interruptible(&random_write_wait);
- kill_fasync(&fasync, SIGIO, POLL_OUT);
- }
+ wake_up_interruptible(&random_write_wait);
+ kill_fasync(&fasync, SIGIO, POLL_OUT);
} else {
_extract_crng(&primary_crng, buf.block);
_crng_backtrack_protect(&primary_crng, buf.block,
@@ -1471,7 +1463,7 @@ static __poll_t random_poll(struct file *file, poll_table *wait)
mask = 0;
if (crng_ready())
mask |= EPOLLIN | EPOLLRDNORM;
- if (input_pool.entropy_count < random_write_wakeup_bits)
+ if (input_pool.entropy_count < POOL_MIN_BITS)
mask |= EPOLLOUT | EPOLLWRNORM;
return mask;
}
@@ -1556,7 +1548,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
*/
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
- if (xchg(&input_pool.entropy_count, 0) && random_write_wakeup_bits) {
+ if (xchg(&input_pool.entropy_count, 0)) {
wake_up_interruptible(&random_write_wait);
kill_fasync(&fasync, SIGIO, POLL_OUT);
}
@@ -1636,9 +1628,9 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
#include <linux/sysctl.h>
-static int min_write_thresh;
-static int max_write_thresh = POOL_BITS;
static int random_min_urandom_seed = 60;
+static int random_write_wakeup_bits = POOL_MIN_BITS;
+static int sysctl_poolsize = POOL_BITS;
static char sysctl_bootid[16];
/*
@@ -1677,7 +1669,6 @@ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer,
return proc_dostring(&fake_table, write, buffer, lenp, ppos);
}
-static int sysctl_poolsize = POOL_BITS;
static struct ctl_table random_table[] = {
{
.procname = "poolsize",
@@ -1698,9 +1689,7 @@ static struct ctl_table random_table[] = {
.data = &random_write_wakeup_bits,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
- .extra1 = &min_write_thresh,
- .extra2 = &max_write_thresh,
+ .proc_handler = proc_dointvec,
},
{
.procname = "urandom_min_reseed_secs",
@@ -1892,13 +1881,13 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
}
/* Throttle writing if we're above the trickle threshold.
- * We'll be woken up again once below random_write_wakeup_thresh,
- * when the calling thread is about to terminate, or once
- * CRNG_RESEED_INTERVAL has lapsed.
+ * We'll be woken up again once below POOL_MIN_BITS, when
+ * the calling thread is about to terminate, or once
+ * CRNG_RESEED_INTERVAL has elapsed.
*/
wait_event_interruptible_timeout(random_write_wait,
!system_wq || kthread_should_stop() ||
- input_pool.entropy_count <= random_write_wakeup_bits,
+ input_pool.entropy_count < POOL_MIN_BITS,
CRNG_RESEED_INTERVAL);
mix_pool_bytes(buffer, count);
credit_entropy_bits(entropy);
--
2.35.1
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