[3.5.y.z extended stable] Patch "random32: fix off-by-one in seeding requirement" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Dec 10 14:27:45 UTC 2013


This is a note to let you know that I have just added a patch titled

    random32: fix off-by-one in seeding requirement

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From b67e6a3d5d9f6322c10a72baaff7f1485726d7ac Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <dborkman at redhat.com>
Date: Mon, 11 Nov 2013 12:20:32 +0100
Subject: random32: fix off-by-one in seeding requirement

commit 51c37a70aaa3f95773af560e6db3073520513912 upstream.

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 at networkplumber.org>
Cc: Florian Weimer <fweimer at redhat.com>
Cc: Theodore Ts'o <tytso at mit.edu>
Signed-off-by: Daniel Borkmann <dborkman at redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes at stressinduktion.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 7e58ad2..54b1fd3 100644
--- 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 938bde5..aa95712 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);
--
1.8.3.2





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