File 0026-lib-uuid-Fix-unseeded-PRNG-on-RANDO.patch of Package u-boot-a20-olinuxino-lime2

Overview Repositories Revisions Requests Users Attributes Meta

File 0026-lib-uuid-Fix-unseeded-PRNG-on-RANDO.patch of Package u-boot-a20-olinuxino-lime2 (Revision 4aec90db10e207322a33b41e4bd45ca3)

Currently displaying revision 4aec90db10e207322a33b41e4bd45ca3 , Show latest

From 28f929297fc0b9c9f817938335981a434c5b234a Mon Sep 17 00:00:00 2001
From: Eugeniu Rosca <erosca@de.adit-jv.com>
Date: Thu, 2 May 2019 14:27:06 +0200
Subject: [PATCH] lib: uuid: Fix unseeded PRNG on RANDOM_UUID=y

The random uuid values (enabled via CONFIG_RANDOM_UUID=y) on our
platform are always the same. Below is consistent on each cold boot:

=> ### interrupt autoboot
 => env default -a; gpt write mmc 1 $partitions; print uuid_gpt_misc
 ...
 uuid_gpt_misc=d117f98e-6f2c-d04b-a5b2-331a19f91cb2
 => env default -a; gpt write mmc 1 $partitions; print uuid_gpt_misc
 ...
 uuid_gpt_misc=ad5ec4b6-2d9f-8544-9417-fe3bd1c9b1b3
 => env default -a; gpt write mmc 1 $partitions; print uuid_gpt_misc
 ...
 uuid_gpt_misc=cceb0b18-39cb-d547-9db7-03b405fa77d4
 => env default -a; gpt write mmc 1 $partitions; print uuid_gpt_misc
 ...
 uuid_gpt_misc=d4981a2b-0478-544e-9607-7fd3c651068d
 => env default -a; gpt write mmc 1 $partitions; print uuid_gpt_misc
 ...
 uuid_gpt_misc=6d6c9a36-e919-264d-a9ee-bd00379686c7

While the uuids do change on every 'gpt write' command, the values
appear to be taken from the same pool, in the same order.

Assuming U-Boot with RANDOM_UUID=y is deployed on a large number of
devices, all those devices would essentially expose the same UUID,
breaking the assumption of system/RFS/application designers who rely
on UUID as being globally unique (e.g. a database using UUID as key
would alias/mix up entries/records due to duplicated UUID).

The root cause seems to be simply _not_ seeding PRNG before generating
a random value. It turns out this belongs to an established class of
PRNG-specific problems, commonly known as "unseeded randomness", for
which I am able to find below bugs/CVE/CWE:
 - https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2015-0285
   ("CVE-2015-0285 openssl: handshake with unseeded PRNG")
 - https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2015-9019
   ("CVE-2015-9019 libxslt: math.random() in xslt uses unseeded
   randomness")
 - https://cwe.mitre.org/data/definitions/336.html
   ("CWE-336: Same Seed in Pseudo-Random Number Generator (PRNG)")

The first revision [1] of this patch updated the seed based on the
output of get_timer(), similar to [4].

There are two problems with this approach:
 - get_timer() has a poor _ms_ resolution
 - when gen_rand_uuid() is called in a loop, get_timer() returns the
   same result, leading to the same seed being passed to srand(),
   leading to the same uuid being generated for several partitions
   with different names

The above drawbacks have been addressed in the second version [2].
In its third revision (current), the patch reworded the description
and summary line to emphasize it is a *fix* rather than an improvement.

Testing [3] consisted of running 'gpt write mmc 1 $partitions' in a
loop on R-Car3 for several minutes, collecting 8844 randomly generated
UUIDS. Two consecutive cold boots are concatenated in the log.
As a result, all uuid values are unique (scripted check).

Thanks to Roman, who reported the issue and provided support in fixing.

[1] https://patchwork.ozlabs.org/patch/1091802/
[2] https://patchwork.ozlabs.org/patch/1092945/
[3] https://gist.github.com/erosca/2820be9d554f76b982edd48474d0e7ca
[4] commit da384a9d7628 ("net: rename and refactor eth_rand_ethaddr() function")

Reported-by: Roman Stratiienko <roman.stratiienko@globallogic.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
(cherry picked from commit 4ccf678f37731d8ec09eae8dca5f4cbe84132a52)
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
---
 lib/uuid.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/uuid.c b/lib/uuid.c
index 5d5adf6b2d..e74d8b110c 100644
--- a/lib/uuid.c
+++ b/lib/uuid.c
@@ -238,6 +238,8 @@ void gen_rand_uuid(unsigned char *uuid_bin)
 	unsigned int *ptr = (unsigned int *)&uuid;
 	int i;
 
+	srand(get_ticks() + rand());
+
 	/* Set all fields randomly */
 	for (i = 0; i < sizeof(struct uuid) / sizeof(*ptr); i++)
 		*(ptr + i) = cpu_to_be32(rand());

Places

File 0026-lib-uuid-Fix-unseeded-PRNG-on-RANDO.patch of Package u-boot-a20-olinuxino-lime2 (Revision 4aec90db10e207322a33b41e4bd45ca3)

Places