linux-kernel - [PATCH] random: only use gathered bytes from arch_get_random

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Date:	Sat, 7 Jul 2012 10:11:22 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	ewust@...ch.edu, zakir@...ch.edu, nadiah@...ucsd.edu,
	jhalderm@...ch.edu, stable@...r.kernel.org
Subject: [PATCH] random: only use gathered bytes from arch_get_random_long

While very unlikely, it is possible for arch_get_random_long() to fail
in the middle of the loop in xfer_secondary_pool(), which would mean
that the loop could stop with only part of u.hwrand populated, leading
to mix_pool_bytes() injecting uninitialized or already injected bytes
instead of fresh bytes. This changes the mix_pool_bytes() call to only
inject the successfully gathered bytes.

Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: stable@...r.kernel.org
---
Should be applied on top of the tytso/random dev branch.
---
 drivers/char/random.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index aaf4629..6fc3128 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -879,7 +879,7 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
 		if (arch_get_random_long(&u.hwrand[i]))
 			break;
 	if (i)
-		mix_pool_bytes(r, &u.hwrand, sizeof(u.hwrand), 0);
+		mix_pool_bytes(r, &u.hwrand, i * sizeof(u.hwrand[0]), 0);
 }
 
 /*
-- 
1.7.0.4

-- 
Kees Cook
Chrome OS Security
--
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