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    Subject[PATCH] (4/4) entropy batching update
    This patch lets the entropy batching pool safely wrap around, allowing
    untrusted samples to be mixed in without risk of flooding out trusted
    samples.

    diff -ur a/drivers/char/random.c b/drivers/char/random.c
    --- a/drivers/char/random.c 2002-08-17 19:55:31.000000000 -0500
    +++ b/drivers/char/random.c 2002-08-17 19:55:38.000000000 -0500
    @@ -596,25 +596,19 @@
    *
    **********************************************************************/

    -static __u32 *batch_entropy_pool;
    -static int *batch_entropy_credit;
    -static int batch_max;
    -static int batch_head, batch_tail;
    +static __u32 *batch_entropy_pool=0;
    +static int batch_max, batch_pos, batch_credit, batch_samples;
    static struct tq_struct batch_tqueue;
    static void batch_entropy_process(void *private_);

    /* note: the size must be a power of 2 */
    static int __init batch_entropy_init(int size, struct entropy_store *r)
    {
    - batch_entropy_pool = kmalloc(2*size*sizeof(__u32), GFP_KERNEL);
    + batch_entropy_pool = kmalloc(size*sizeof(__u32), GFP_KERNEL);
    if (!batch_entropy_pool)
    return -1;
    - batch_entropy_credit =kmalloc(size*sizeof(int), GFP_KERNEL);
    - if (!batch_entropy_credit) {
    - kfree(batch_entropy_pool);
    - return -1;
    - }
    - batch_head = batch_tail = 0;
    +
    + batch_pos = batch_credit = batch_samples = 0;
    batch_max = size;
    batch_tqueue.routine = batch_entropy_process;
    batch_tqueue.data = r;
    @@ -622,57 +616,61 @@
    }

    /*
    - * Changes to the entropy data is put into a queue rather than being
    + * Changes to the entropy data are put into a queue rather than being
    * added to the entropy counts directly. This is to avoid doing heavy
    * hashing calculations during an interrupt in add_timing_entropy().
    * Instead, the entropy is only added to the pool once per timer tick.
    + *
    + * The batch pool intentionally allows wrap-around, to protect against
    + * flooding of untrusted data. Non-random data will not correlate with
    + * random data and can be safely XORed over existing data.
    */

    -void batch_entropy_store(u32 a, u32 b, int num)
    +void batch_entropy_store(u32 val, int bits)
    {
    - int new;
    -
    if (!batch_max)
    return;

    - batch_entropy_pool[2*batch_head] = a;
    - batch_entropy_pool[(2*batch_head) + 1] = b;
    - batch_entropy_credit[batch_head] = num;
    -
    - new = (batch_head+1) & (batch_max-1);
    - if (new != batch_tail) {
    - queue_task(&batch_tqueue, &tq_timer);
    - batch_head = new;
    - } else {
    - DEBUG_ENT("batch entropy buffer full\n");
    - }
    + batch_entropy_pool[batch_pos] ^= val;
    + batch_credit+=bits;
    + batch_samples++;
    + batch_pos = (batch_pos+1) & (batch_max-1);
    +
    + queue_task(&batch_tqueue, &tq_timer);
    }

    /*
    - * Flush out the accumulated entropy operations, adding entropy to the passed
    - * store (normally random_state). If that store has enough entropy, alternate
    - * between randomizing the data of the primary and secondary stores.
    + * Flush out the accumulated entropy operations, adding entropy to the
    + * passed store (normally random_state). Alternate between randomizing
    + * the data of the primary and secondary stores.
    */
    static void batch_entropy_process(void *private_)
    {
    - struct entropy_store *r = (struct entropy_store *) private_, *p;
    - int max_entropy = r->poolinfo.POOLBITS;
    -
    + struct entropy_store *r = (struct entropy_store *) private_;
    + int samples, credit;
    +
    if (!batch_max)
    return;

    - p = r;
    - while (batch_head != batch_tail) {
    - if (r->entropy_count >= max_entropy) {
    - r = (r == sec_random_state) ? random_state :
    - sec_random_state;
    - max_entropy = r->poolinfo.POOLBITS;
    - }
    - add_entropy_words(r, batch_entropy_pool + 2*batch_tail, 2);
    - credit_entropy_store(r, batch_entropy_credit[batch_tail]);
    - batch_tail = (batch_tail+1) & (batch_max-1);
    + /* switch pools if current full */
    + if (r->entropy_count >= r->poolinfo.POOLBITS) {
    + r = (r == sec_random_state) ?
    + random_state : sec_random_state;
    }
    - if (p->entropy_count >= random_read_wakeup_thresh)
    +
    + credit=batch_credit;
    + samples=batch_samples;
    + batch_pos = batch_credit = batch_samples = 0;
    +
    + /* Don't allow more credit BITS > pool WORDS */
    + if(credit > batch_max) credit=batch_max;
    + /* Check for pool wrap-around */
    + if(samples > batch_max) samples=batch_max;
    +
    + add_entropy_words(r, batch_entropy_pool, samples);
    + credit_entropy_store(r, credit);
    +
    + if (r->entropy_count >= random_read_wakeup_thresh)
    wake_up_interruptible(&random_read_wait);
    }

    @@ -766,7 +764,7 @@
    delta>>=es->shift;
    bits=benford[int_log2_16bits(delta & 0xffff)];
    }
    - batch_entropy_store(datum, time, bits);
    + batch_entropy_store(datum^time, bits);
    }

    /******************************************************************
    diff -ur a/include/linux/random.h b/include/linux/random.h
    --- a/include/linux/random.h 2002-08-17 19:55:31.000000000 -0500
    +++ b/include/linux/random.h 2002-08-17 19:55:38.000000000 -0500
    @@ -44,7 +44,7 @@

    extern void rand_initialize(void);

    -extern void batch_entropy_store(u32 a, u32 b, int num);
    +extern void batch_entropy_store(u32 val, int bits);
    extern void *create_entropy_source(int granularity_khz);
    extern void free_entropy_source(void *src);
    extern void add_timing_entropy(void *src, unsigned datum);
    --
    "Love the dolphins," she advised him. "Write by W.A.S.T.E.."
    -
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