From: Matt Mackall <mpm@selenic.com>
Additional parameter to allow keeping an entropy reserve in the input pool.
Groundwork for proper /dev/urandom vs /dev/random starvation prevention.
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/drivers/char/random.c | 30 +++++++++++++++++-------------
1 files changed, 17 insertions(+), 13 deletions(-)
diff -puN drivers/char/random.c~random-pt3-entropy-reservation-accounting drivers/char/random.c
--- 25/drivers/char/random.c~random-pt3-entropy-reservation-accounting 2005-02-22 18:17:04.000000000 -0800
+++ 25-akpm/drivers/char/random.c 2005-02-22 18:17:04.000000000 -0800
@@ -1183,7 +1183,7 @@ static void MD5Transform(__u32 buf[HASH_
#define SEC_XFER_SIZE (TMP_BUF_SIZE*4)
static ssize_t extract_entropy(struct entropy_store *r, void * buf,
- size_t nbytes, int min, int flags);
+ size_t nbytes, int min, int rsvd, int flags);
/*
* This utility inline function is responsible for transfering entropy
@@ -1203,7 +1203,7 @@ static inline void xfer_secondary_pool(s
r->name, bytes * 8, nbytes * 8, r->entropy_count);
bytes=extract_entropy(&input_pool, tmp, bytes,
- random_read_wakeup_thresh / 8,
+ random_read_wakeup_thresh / 8, 0,
EXTRACT_ENTROPY_LIMIT);
add_entropy_words(r, tmp, (bytes + 3) / 4);
credit_entropy_store(r, bytes*8);
@@ -1221,13 +1221,15 @@ static inline void xfer_secondary_pool(s
* extracting entropy from the secondary pool, and can refill from the
* primary pool if needed.
*
- * If we have less than min bytes of entropy available, exit without
- * transferring any. This helps avoid racing when reseeding.
+ * The min parameter specifies the minimum amount we can pull before
+ * failing to avoid races that defeat catastrophic reseeding while the
+ * reserved parameter indicates how much entropy we must leave in the
+ * pool after each pull to avoid starving other readers.
*
* Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
*/
static ssize_t extract_entropy(struct entropy_store *r, void * buf,
- size_t nbytes, int min, int flags)
+ size_t nbytes, int min, int reserved, int flags)
{
ssize_t ret, i;
__u32 tmp[TMP_BUF_SIZE], data[16];
@@ -1247,17 +1249,19 @@ static ssize_t extract_entropy(struct en
DEBUG_ENT("trying to extract %d bits from %s\n",
nbytes * 8, r->name);
- if (r->entropy_count / 8 < min) {
+ /* Can we pull enough? */
+ if (r->entropy_count / 8 < min + reserved) {
nbytes = 0;
} else {
+ /* If limited, never pull more than available */
if (flags & EXTRACT_ENTROPY_LIMIT &&
- nbytes >= r->entropy_count / 8)
- nbytes = r->entropy_count / 8;
+ nbytes + reserved >= r->entropy_count / 8)
+ nbytes = r->entropy_count/8 - reserved;
- if (r->entropy_count / 8 >= nbytes)
+ if(r->entropy_count / 8 >= nbytes + reserved)
r->entropy_count -= nbytes*8;
else
- r->entropy_count = 0;
+ r->entropy_count = reserved;
if (r->entropy_count < random_write_wakeup_thresh)
wake_up_interruptible(&random_write_wait);
@@ -1354,7 +1358,7 @@ static ssize_t extract_entropy(struct en
*/
void get_random_bytes(void *buf, int nbytes)
{
- extract_entropy(&nonblocking_pool, (char *) buf, nbytes, 0,
+ extract_entropy(&nonblocking_pool, (char *) buf, nbytes, 0, 0,
EXTRACT_ENTROPY_SECONDARY);
}
@@ -1444,7 +1448,7 @@ random_read(struct file * file, char __u
DEBUG_ENT("reading %d bits\n", n*8);
- n = extract_entropy(&blocking_pool, buf, n, 0,
+ n = extract_entropy(&blocking_pool, buf, n, 0, 0,
EXTRACT_ENTROPY_USER |
EXTRACT_ENTROPY_LIMIT |
EXTRACT_ENTROPY_SECONDARY);
@@ -1506,7 +1510,7 @@ urandom_read(struct file * file, char __
flags |= EXTRACT_ENTROPY_SECONDARY;
spin_unlock_irqrestore(&input_pool.lock, cpuflags);
- return extract_entropy(&nonblocking_pool, buf, nbytes, 0, flags);
+ return extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0, flags);
}
static unsigned int
_