random32: add periodic reseeding
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>
diff --git a/lib/random32.c b/lib/random32.c
index 01e8890..12215df 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -142,6 +142,7 @@
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 @@
}
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 @@
/* mix it in */
prandom_u32_state(state);
}
+ prandom_start_seed_timer();
return 0;
}
late_initcall(prandom_reseed);