From: "Theodore Ts'o" <tytso@mit.edu>
This patch adds a separate pool for use with /dev/urandom. This prevents a
/dev/urandom read from being able to completely drain the entropy in the
/dev/random pool, and also makes it much more difficult for an attacker to
carry out a state extension attack.
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/drivers/char/random.c | 36 +++++++++++++++++++++++++++---------
1 files changed, 27 insertions(+), 9 deletions(-)
diff -puN drivers/char/random.c~dev-random-use-separate-entropy-store-for-dev-urandom drivers/char/random.c
--- 25/drivers/char/random.c~dev-random-use-separate-entropy-store-for-dev-urandom 2004-08-19 23:36:20.239635000 -0700
+++ 25-akpm/drivers/char/random.c 2004-08-19 23:36:20.244634240 -0700
@@ -401,6 +401,7 @@ static struct poolinfo {
*/
static struct entropy_store *random_state; /* The default global store */
static struct entropy_store *sec_random_state; /* secondary store */
+static struct entropy_store *urandom_state; /* For urandom */
static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
@@ -1467,14 +1468,21 @@ static ssize_t extract_entropy(struct en
*/
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
+ struct entropy_store *r = urandom_state;
+ int flags = EXTRACT_ENTROPY_SECONDARY;
+
+ if (!r)
+ r = sec_random_state;
+ if (!r) {
+ r = random_state;
+ flags = 0;
+ }
+ if (!r) {
printk(KERN_NOTICE "get_random_bytes called before "
"random driver initialization\n");
+ return;
+ }
+ extract_entropy(r, (char *) buf, nbytes, flags);
}
EXPORT_SYMBOL(get_random_bytes);
@@ -1525,8 +1533,12 @@ static int __init rand_initialize(void)
if (create_entropy_store(SECONDARY_POOL_SIZE, "secondary",
&sec_random_state))
goto err;
+ if (create_entropy_store(SECONDARY_POOL_SIZE, "urandom",
+ &urandom_state))
+ goto err;
clear_entropy_store(random_state);
clear_entropy_store(sec_random_state);
+ clear_entropy_store(urandom_state);
init_std_data(random_state);
init_std_data(sec_random_state);
#ifdef CONFIG_SYSCTL
@@ -1661,9 +1673,15 @@ static ssize_t
urandom_read(struct file * file, char __user * buf,
size_t nbytes, loff_t *ppos)
{
- return extract_entropy(sec_random_state, buf, nbytes,
- EXTRACT_ENTROPY_USER |
- EXTRACT_ENTROPY_SECONDARY);
+ int flags = EXTRACT_ENTROPY_USER;
+ unsigned long cpuflags;
+
+ spin_lock_irqsave(&random_state->lock, cpuflags);
+ if (random_state->entropy_count > random_state->poolinfo.POOLBITS)
+ flags |= EXTRACT_ENTROPY_SECONDARY;
+ spin_unlock_irqrestore(&random_state->lock, cpuflags);
+
+ return extract_entropy(urandom_state, buf, nbytes, flags);
}
static unsigned int
_