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random32: add periodic reseeding

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The current Tausworthe PRNG is never reseeded with truly random data after
the first attempt in late_initcall. As this PRNG is used for some critical
random data as e.g. UDP port randomization we should try better and reseed
the PRNG once in a while with truly random data from get_random_bytes().

When we reseed with prandom_seed we now make also sure to throw the first
output away. This suffices the reseeding procedure.

The delay calculation is based on a proposal from Eric Dumazet.

Joint work with Daniel Borkmann.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hannes Frederic Sowa 2013-11-11 12:20:33 +01:00 committed by David S. Miller
parent 51c37a70aa
commit 6d31920246
1 changed files with 23 additions and 0 deletions
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23
lib/random32.c
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@ -142,6 +142,7 @@ void prandom_seed(u32 entropy)
for_each_possible_cpu (i) {
struct rnd_state *state = &per_cpu(net_rand_state, i);
state->s1 = __seed(state->s1 ^ entropy, 2);
prandom_u32_state(state);
}
}
EXPORT_SYMBOL(prandom_seed);
@ -174,6 +175,27 @@ static int __init prandom_init(void)
}
core_initcall(prandom_init);
static void __prandom_timer(unsigned long dontcare);
static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
static void __prandom_timer(unsigned long dontcare)
{
u32 entropy;
get_random_bytes(&entropy, sizeof(entropy));
prandom_seed(entropy);
/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
seed_timer.expires = jiffies + (40 * HZ + (prandom_u32() % (40 * HZ)));
add_timer(&seed_timer);
}
static void prandom_start_seed_timer(void)
{
set_timer_slack(&seed_timer, HZ);
seed_timer.expires = jiffies + 40 * HZ;
add_timer(&seed_timer);
}
/*
* Generate better values after random number generator
* is fully initialized.
@ -194,6 +216,7 @@ static int __init prandom_reseed(void)
/* mix it in */
prandom_u32_state(state);
}
prandom_start_seed_timer();
return 0;
}
late_initcall(prandom_reseed);