[PATCH] random: only use gathered bytes from arch_get_random_long

Kees Cook
2012-07-07T17:11:29Z

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@chromium.org>
Cc: stable@vger.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