From 12516ee18158670b880446cedb4a88a144702928 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Mon, 11 Nov 2013 12:20:32 +0100 Subject: random32: fix off-by-one in seeding requirement [ Upstream commit 51c37a70aaa3f95773af560e6db3073520513912 ] 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 Signed-off-by: Ben Hutchings --- 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 7e77cee62bd9..f5e1311f491e 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -89,9 +89,9 @@ static inline void prandom32_seed(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 fc3545a32771..1f44bdc6e8d3 100644 --- a/lib/random32.c +++ b/lib/random32.c @@ -92,7 +92,7 @@ void srandom32(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(srandom32); @@ -109,9 +109,9 @@ static int __init random32_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" */ prandom32(state); @@ -138,9 +138,9 @@ static int __init random32_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 */ prandom32(state); -- cgit v1.2.3