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random32: seeding improvement
The rationale is: * use u32 consistently * no need to do LCG on values from (better) get_random_bytes * use more data from get_random_bytes for secondary seeding * don't reduce state space on srandom32() * enforce state variable initialization restrictions Note: the second paper has a version of random32() with even longer period and a version of random64() if needed. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -56,23 +56,12 @@ static u32 __random32(struct rnd_state *state)
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return (state->s1 ^ state->s2 ^ state->s3);
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}
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static void __set_random32(struct rnd_state *state, unsigned long s)
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/*
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* Handle minimum values for seeds
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*/
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static inline u32 __seed(u32 x, u32 m)
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{
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if (s == 0)
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s = 1; /* default seed is 1 */
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#define LCG(n) (69069 * n)
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state->s1 = LCG(s);
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state->s2 = LCG(state->s1);
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state->s3 = LCG(state->s2);
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/* "warm it up" */
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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return (x < m) ? x + m : x;
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}
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/**
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@ -107,7 +96,7 @@ void srandom32(u32 entropy)
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*/
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for_each_possible_cpu (i) {
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struct rnd_state *state = &per_cpu(net_rand_state, i);
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__set_random32(state, state->s1 ^ entropy);
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state->s1 = __seed(state->s1 ^ entropy, 1);
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}
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}
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EXPORT_SYMBOL(srandom32);
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@ -122,7 +111,19 @@ static int __init random32_init(void)
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for_each_possible_cpu(i) {
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struct rnd_state *state = &per_cpu(net_rand_state,i);
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__set_random32(state, i + jiffies);
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#define LCG(x) ((x) * 69069) /* super-duper LCG */
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state->s1 = __seed(LCG(i + jiffies), 1);
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state->s2 = __seed(LCG(state->s1), 7);
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state->s3 = __seed(LCG(state->s2), 15);
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/* "warm it up" */
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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}
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return 0;
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}
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@ -135,13 +136,18 @@ core_initcall(random32_init);
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static int __init random32_reseed(void)
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{
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int i;
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unsigned long seed;
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for_each_possible_cpu(i) {
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struct rnd_state *state = &per_cpu(net_rand_state,i);
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u32 seeds[3];
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get_random_bytes(&seed, sizeof(seed));
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__set_random32(state, seed);
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get_random_bytes(&seeds, sizeof(seeds));
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state->s1 = __seed(seeds[0], 1);
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state->s2 = __seed(seeds[1], 7);
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state->s3 = __seed(seeds[2], 15);
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/* mix it in */
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__random32(state);
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}
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return 0;
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}
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