[ovs-dev] [PATCH 3/3] random: Get random seed from /dev/urandom.

Justin Pettit jpettit at nicira.com
Thu Aug 12 21:34:07 UTC 2010


Looks good.

--Justin


On Aug 12, 2010, at 11:12 AM, Ben Pfaff wrote:

> diff --git a/lib/random.c b/lib/random.c
> index 78a5916..88ddb4a 100644
> --- a/lib/random.c
> +++ b/lib/random.c
> @@ -21,6 +21,7 @@
> #include <stdlib.h>
> #include <sys/time.h>
> 
> +#include "entropy.h"
> #include "util.h"
> 
> /* This is the 32-bit PRNG recommended in G. Marsaglia, "Xorshift RNGs",
> @@ -29,7 +30,10 @@
>  *
>  * We use this PRNG instead of libc's rand() because rand() varies in quality
>  * and because its maximum value also varies between 32767 and INT_MAX, whereas
> - * we often want random numbers in the full range of uint32_t.  */
> + * we often want random numbers in the full range of uint32_t.
> + *
> + * This random number generator is intended for purposes that do not require
> + * cryptographic-quality randomness. */
> 
> /* Current random state. */
> static uint32_t seed;
> @@ -39,19 +43,16 @@ static uint32_t random_next(void);
> void
> random_init(void)
> {
> -    if (!seed) {
> +    while (!seed) {
>         struct timeval tv;
> +        uint32_t entropy;
> 
>         if (gettimeofday(&tv, NULL) < 0) {
>             ovs_fatal(errno, "gettimeofday");
>         }
> +        get_entropy_or_die(&entropy, 4);
> 
> -        seed = tv.tv_sec ^ tv.tv_usec;
> -        if (!seed) {
> -            /* A 'seed' of 0 is fatal to randomness--the random value will
> -             * always be 0--so use the initial seed mentioned by Marsaglia. */
> -            seed = UINT32_C(2463534242);
> -        }
> +        seed = tv.tv_sec ^ tv.tv_usec ^ entropy;
>     }
> }
> 
> -- 
> 1.7.1
> 
> 
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