From 51c37a70aaa3f95773af560e6db3073520513912 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Mon, 11 Nov 2013 12:20:32 +0100 Subject: [PATCH] random32: fix off-by-one in seeding requirement For properly initialising the Tausworthe generator [1], we have a strict seeding requirement, that is, s1 > 1, s2 > 7, s3 > 15. Commit 697f8d0348 ("random32: seeding improvement") introduced a __seed() function that imposes boundary checks proposed by the errata paper [2] to properly ensure above conditions. However, we're off by one, as the function is implemented as: "return (x < m) ? x + m : x;", and called with __seed(X, 1), __seed(X, 7), __seed(X, 15). Thus, an unwanted seed of 1, 7, 15 would be possible, whereas the lower boundary should actually be of at least 2, 8, 16, just as GSL does. Fix this, as otherwise an initialization with an unwanted seed could have the effect that Tausworthe's PRNG properties cannot not be ensured. Note that this PRNG is *not* used for cryptography in the kernel. [1] http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps [2] http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps Joint work with Hannes Frederic Sowa. Fixes: 697f8d0348a6 ("random32: seeding improvement") Cc: Stephen Hemminger Cc: Florian Weimer Cc: Theodore Ts'o Signed-off-by: Daniel Borkmann Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- include/linux/random.h | 6 +++--- lib/random32.c | 14 +++++++------- 2 files changed, 10 insertions(+), 10 deletions(-) diff --git a/include/linux/random.h b/include/linux/random.h index 6312dd9ba449..bf9085e89fb5 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -50,9 +50,9 @@ static inline void prandom_seed_state(struct rnd_state *state, u64 seed) { u32 i = (seed >> 32) ^ (seed << 10) ^ seed; - state->s1 = __seed(i, 1); - state->s2 = __seed(i, 7); - state->s3 = __seed(i, 15); + state->s1 = __seed(i, 2); + state->s2 = __seed(i, 8); + state->s3 = __seed(i, 16); } #ifdef CONFIG_ARCH_RANDOM diff --git a/lib/random32.c b/lib/random32.c index 52280d5526be..01e8890d1089 100644 --- a/lib/random32.c +++ b/lib/random32.c @@ -141,7 +141,7 @@ 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, 1); + state->s1 = __seed(state->s1 ^ entropy, 2); } } EXPORT_SYMBOL(prandom_seed); @@ -158,9 +158,9 @@ static int __init prandom_init(void) struct rnd_state *state = &per_cpu(net_rand_state,i); #define LCG(x) ((x) * 69069) /* super-duper LCG */ - state->s1 = __seed(LCG(i + jiffies), 1); - state->s2 = __seed(LCG(state->s1), 7); - state->s3 = __seed(LCG(state->s2), 15); + state->s1 = __seed(LCG(i + jiffies), 2); + state->s2 = __seed(LCG(state->s1), 8); + state->s3 = __seed(LCG(state->s2), 16); /* "warm it up" */ prandom_u32_state(state); @@ -187,9 +187,9 @@ static int __init prandom_reseed(void) u32 seeds[3]; get_random_bytes(&seeds, sizeof(seeds)); - state->s1 = __seed(seeds[0], 1); - state->s2 = __seed(seeds[1], 7); - state->s3 = __seed(seeds[2], 15); + state->s1 = __seed(seeds[0], 2); + state->s2 = __seed(seeds[1], 8); + state->s3 = __seed(seeds[2], 16); /* mix it in */ prandom_u32_state(state); -- 2.39.5