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 <stephen@networkplumber.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/random.h b/include/linux/random.h
index 7e58ad27b7ffb00bd4d45efa3688d8bfcd37464f..54b1fd3efdfa17071b737d5aba5c1e5b8a5ef92e 100644 (file)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -87,9 +87,9 @@ 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 938bde5876ac43aa4b1cb316b4e074f66ee2271f..aa95712c1431fb79ee4fa67135176c816093f76e 100644 (file)
--- 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);