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Subject[PATCH 9/11] Entropy fixes - refactor reseeding
Factor pool reseeding out of normal entropy transfer. This allows
different pools to have different policy on how to reseed.

This patch also makes random_read actually use the entropy count in
the secondary pool rather than tracking off the primary.

diff -urN clean/drivers/char/random.c patched/drivers/char/random.c
--- clean/drivers/char/random.c 2002-09-10 23:32:04.000000000 -0500
+++ patched/drivers/char/random.c 2002-09-10 23:34:28.000000000 -0500
@@ -886,7 +886,6 @@
*********************************************************************/

#define EXTRACT_ENTROPY_USER 1
-#define EXTRACT_ENTROPY_SECONDARY 2
#define TMP_BUF_SIZE (HASH_BUFFER_SIZE + HASH_EXTRA_SIZE)
#define SEC_XFER_SIZE (TMP_BUF_SIZE*4)

@@ -928,10 +927,6 @@
* number of bytes that are actually obtained. If the EXTRACT_ENTROPY_USER
* flag is given, then the buf pointer is assumed to be in user space.
*
- * If the EXTRACT_ENTROPY_SECONDARY flag is given, then we are actually
- * extracting entropy from the secondary pool, and can refill from the
- * primary pool if needed.
- *
* Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
*/
static ssize_t extract_entropy(struct entropy_store *r, void * buf,
@@ -945,9 +940,6 @@
if (r->entropy_count > r->poolinfo.POOLBITS)
r->entropy_count = r->poolinfo.POOLBITS;

- if (flags & EXTRACT_ENTROPY_SECONDARY)
- xfer_secondary_pool(r, nbytes);
-
DEBUG_ENT("%s has %d bits, want %d bits\n",
r == sec_random_state ? "secondary" :
r == random_state ? "primary" : "unknown",
@@ -1029,6 +1021,18 @@
return ret;
}

+/* Reseed pool with pull bits from input pool, provided input pool has
+ * more than thresh bits available. Pull should be sufficient for a
+ * "catastrophic reseed" - enough to make the destination pool
+ * unguessable should it be compromised
+ */
+void reseed_pool(struct entropy_store *r, int thresh, int pull)
+{
+ if (r->entropy_count < 8 &&
+ random_state->entropy_count > thresh)
+ xfer_secondary_pool(r, pull/8);
+}
+
/*
* This function is the exported kernel interface. It returns some
* number of good random numbers, suitable for seeding TCP sequence
@@ -1036,14 +1040,16 @@
*/
void get_random_bytes(void *buf, int nbytes)
{
- if (sec_random_state)
- extract_entropy(sec_random_state, (char *) buf, nbytes,
- EXTRACT_ENTROPY_SECONDARY);
- else if (random_state)
- extract_entropy(random_state, (char *) buf, nbytes, 0);
- else
+ if (!sec_random_state)
+ {
printk(KERN_NOTICE "get_random_bytes called before "
"random driver initialization\n");
+ return;
+ }
+
+ reseed_pool(sec_random_state,
+ random_read_wakeup_thresh, random_read_wakeup_thresh);
+ extract_entropy(sec_random_state, (char *) buf, nbytes, 0);
}

/*********************************************************************
@@ -1107,14 +1113,19 @@
return 0;

add_wait_queue(&random_read_wait, &wait);
+
while (nbytes > 0) {
set_current_state(TASK_INTERRUPTIBLE);

+ reseed_pool(sec_random_state,
+ random_read_wakeup_thresh,
+ random_read_wakeup_thresh);
+
n = nbytes;
if (n > SEC_XFER_SIZE)
n = SEC_XFER_SIZE;
- if (n > random_state->entropy_count / 8)
- n = random_state->entropy_count / 8;
+ if (n > sec_random_state->entropy_count / 8)
+ n = sec_random_state->entropy_count / 8;
if (n == 0) {
if (file->f_flags & O_NONBLOCK) {
retval = -EAGAIN;
@@ -1133,8 +1144,8 @@
sec_random_state->entropy_count);

n = extract_entropy(sec_random_state, buf, n,
- EXTRACT_ENTROPY_USER |
- EXTRACT_ENTROPY_SECONDARY);
+ EXTRACT_ENTROPY_USER);
+
if (n < 0) {
retval = n;
break;
@@ -1162,9 +1173,11 @@
urandom_read(struct file * file, char * buf,
size_t nbytes, loff_t *ppos)
{
+ reseed_pool(sec_random_state,
+ random_read_wakeup_thresh, random_read_wakeup_thresh);
+
return extract_entropy(sec_random_state, buf, nbytes,
- EXTRACT_ENTROPY_USER |
- EXTRACT_ENTROPY_SECONDARY);
+ EXTRACT_ENTROPY_USER);
}

static unsigned int

--
"Love the dolphins," she advised him. "Write by W.A.S.T.E.."
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