random32: add periodic reseeding (6d319202) · Commits · 戴 / test

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>

lib/random32.c

+23 −0

Original line number	Diff line number	Diff line
		@@ -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);

Admin message