linux-kernel - [v2.6.34-stable 162/165] random: Add comment to random

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Date:	Wed, 15 Aug 2012 15:48:26 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:	Tony Luck <tony.luck@...el.com>, "Theodore Ts'o" <tytso@....edu>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [v2.6.34-stable 162/165] random: Add comment to random_initialize()

From: Tony Luck <tony.luck@...el.com>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit cbc96b7594b5691d61eba2db8b2ea723645be9ca upstream.

Many platforms have per-machine instance data (serial numbers,
asset tags, etc.) squirreled away in areas that are accessed
during early system bringup. Mixing this data into the random
pools has a very high value in providing better random data,
so we should allow (and even encourage) architecture code to
call add_device_randomness() from the setup_arch() paths.

However, this limits our options for internal structure of
the random driver since random_initialize() is not called
until long after setup_arch().

Add a big fat comment to rand_initialize() spelling out
this requirement.

Suggested-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 drivers/char/random.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1644b8e..7e19406 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1088,6 +1088,16 @@ static void init_std_data(struct entropy_store *r)
 	mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
 }
 
+/*
+ * Note that setup_arch() may call add_device_randomness()
+ * long before we get here. This allows seeding of the pools
+ * with some platform dependent data very early in the boot
+ * process. But it limits our options here. We must use
+ * statically allocated structures that already have all
+ * initializations complete at compile time. We should also
+ * take care not to overwrite the precious per platform data
+ * we were given.
+ */
 static int rand_initialize(void)
 {
 	init_std_data(&input_pool);
-- 
1.7.12.rc2

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