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Subject[PATCH 1/6] random: Addition of kernel_pool
Date
The kernel pool is intended to serve kernel-internal callers only.
Its purpose and usage is identical to the blocking_pool.

As the kernel_pool is not available to user space, user space cannot
directly interfere with the blocking behavior when obtaining
data from the kernel_pool. Thus, if entropy is present in the
kernel_pool, user space can hog /dev/random and yet the kernel
internal requestor of random numbers that are generated equally
to the blocking_pool (i.e. with the blocking behavior) will not
be affected until data is needed from the input_pool.

The patch treats the kernel_pool fully equally to the blocking and
nonblocking pool with respect to the initialization and update. As now
there are three output pools, the patch adds a round-robin logic for
processing additional entropy when the input_pool is nearly full.

CC: Andreas Steffen <andreas.steffen@strongswan.org>
CC: Theodore Ts'o <tytso@mit.edu>
CC: Sandy Harris <sandyinchina@gmail.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
drivers/char/random.c | 52 ++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 9cd6968..2868754 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -407,6 +407,7 @@ static struct poolinfo {
static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
static DECLARE_WAIT_QUEUE_HEAD(urandom_init_wait);
+static DECLARE_WAIT_QUEUE_HEAD(random_kernel_wait);
static struct fasync_struct *fasync;

/**********************************************************************
@@ -442,6 +443,7 @@ static void push_to_pool(struct work_struct *work);
static __u32 input_pool_data[INPUT_POOL_WORDS];
static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
+static __u32 kernel_pool_data[OUTPUT_POOL_WORDS];

static struct entropy_store input_pool = {
.poolinfo = &poolinfo_table[0],
@@ -472,6 +474,17 @@ static struct entropy_store nonblocking_pool = {
push_to_pool),
};

+static struct entropy_store kernel_pool = {
+ .poolinfo = &poolinfo_table[1],
+ .name = "kernel",
+ .limit = 1,
+ .pull = &input_pool,
+ .lock = __SPIN_LOCK_UNLOCKED(kernel_pool.lock),
+ .pool = kernel_pool_data,
+ .push_work = __WORK_INITIALIZER(kernel_pool.push_work,
+ push_to_pool),
+};
+
static __u32 const twist_table[8] = {
0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
@@ -674,29 +687,41 @@ retry:

/* should we wake readers? */
if (entropy_bits >= random_read_wakeup_bits) {
+ wake_up_interruptible(&random_kernel_wait);
wake_up_interruptible(&random_read_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
}
/* If the input pool is getting full, send some
- * entropy to the two output pools, flipping back and
+ * entropy to the output pools, flipping back and
* forth between them, until the output pools are 75%
* full.
*/
if (entropy_bits > random_write_wakeup_bits &&
r->initialized &&
r->entropy_total >= 2*random_read_wakeup_bits) {
- static struct entropy_store *last = &blocking_pool;
- struct entropy_store *other = &blocking_pool;
-
- if (last == &blocking_pool)
- other = &nonblocking_pool;
- if (other->entropy_count <=
- 3 * other->poolinfo->poolfracbits / 4)
- last = other;
- if (last->entropy_count <=
- 3 * last->poolinfo->poolfracbits / 4) {
- schedule_work(&last->push_work);
- r->entropy_total = 0;
+#define NUM_OUTPUT_POOLS 3
+ /* as we will recalculate this variable first thing in
+ * the loop, it will point to the first output pool
+ * after the first recalculation */
+ static int selected_pool = (NUM_OUTPUT_POOLS - 1);
+ int i = 0;
+ struct entropy_store *output_pools[NUM_OUTPUT_POOLS] = {
+ &blocking_pool,
+ &nonblocking_pool,
+ &kernel_pool};
+ /* select the next pool that has less than 75% fill
+ * rate */
+ for (i = 0; NUM_OUTPUT_POOLS > i; i++) {
+ struct entropy_store *p = NULL;
+ selected_pool =
+ (selected_pool + 1) % NUM_OUTPUT_POOLS;
+ p = output_pools[selected_pool];
+ if (p->entropy_count <=
+ p->poolinfo->poolfracbits / 4) {
+ schedule_work(&p->push_work);
+ r->entropy_total = 0;
+ break;
+ }
}
}
}
@@ -1318,6 +1343,7 @@ static int rand_initialize(void)
init_std_data(&input_pool);
init_std_data(&blocking_pool);
init_std_data(&nonblocking_pool);
+ init_std_data(&kernel_pool);
return 0;
}
early_initcall(rand_initialize);
--
2.1.0



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