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SubjectRe: Seeding /dev/random not working
On Tue, May 29, 2007 at 12:46:14PM -0500, Matt Mackall wrote:
> We might as well mix jiffies and cycles in at init time in a manner
> similar to the above. Something like this (untested):

Scratch that one. Here's one that compiles and seems to work under
lguest:

Index: l/drivers/char/random.c
===================================================================
--- l.orig/drivers/char/random.c 2007-05-29 12:45:00.000000000 -0500
+++ l/drivers/char/random.c 2007-05-29 12:50:02.000000000 -0500
@@ -559,6 +559,26 @@ static struct timer_rand_state input_tim
static struct timer_rand_state *irq_timer_state[NR_IRQS];

/*
+ * Mix a sample of the current time into the pool with no entropy
+ * accounting
+ */
+static long __add_timer_randomness(unsigned num)
+{
+ struct {
+ cycles_t cycles;
+ long jiffies;
+ unsigned num;
+ } sample;
+
+ sample.jiffies = jiffies;
+ sample.cycles = get_cycles();
+ sample.num = num;
+ add_entropy_words(&input_pool, (u32 *)&sample, sizeof(sample)/4);
+
+ return sample.jiffies;
+}
+
+/*
* This function adds entropy to the entropy "pool" by using timing
* delays. It uses the timer_rand_state structure to make an estimate
* of how many bits of entropy this call has added to the pool.
@@ -570,12 +590,7 @@ static struct timer_rand_state *irq_time
*/
static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
{
- struct {
- cycles_t cycles;
- long jiffies;
- unsigned num;
- } sample;
- long delta, delta2, delta3;
+ long timestamp, delta, delta2, delta3;

preempt_disable();
/* if over the trickle threshold, use only 1 in 4096 samples */
@@ -583,10 +598,7 @@ static void add_timer_randomness(struct
(__get_cpu_var(trickle_count)++ & 0xfff))
goto out;

- sample.jiffies = jiffies;
- sample.cycles = get_cycles();
- sample.num = num;
- add_entropy_words(&input_pool, (u32 *)&sample, sizeof(sample)/4);
+ timestamp = __add_timer_randomness(num);

/*
* Calculate number of bits of randomness we probably added.
@@ -595,8 +607,8 @@ static void add_timer_randomness(struct
*/

if (!state->dont_count_entropy) {
- delta = sample.jiffies - state->last_time;
- state->last_time = sample.jiffies;
+ delta = timestamp - state->last_time;
+ state->last_time = timestamp;

delta2 = delta - state->last_delta;
state->last_delta = delta;
@@ -899,6 +911,7 @@ static int __init rand_initialize(void)
init_std_data(&input_pool);
init_std_data(&blocking_pool);
init_std_data(&nonblocking_pool);
+ __add_timer_randomness(0);
return 0;
}
module_init(rand_initialize);
@@ -1028,6 +1041,8 @@ random_write(struct file * file, const c
const char __user *p = buffer;
size_t c = count;

+ __add_timer_randomness(0);
+
while (c > 0) {
bytes = min(c, sizeof(buf));

--
Mathematics is the supreme nostalgia of our time.
-
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