From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, George Spelvin , Theodore Tso , Linus Torvalds Subject: [PATCH 3.19 009/175] random: Fix fast_mix() function Date: Tue, 3 Mar 2015 22:13:07 -0800 Message-Id: <20150304061027.840948908@linuxfoundation.org> In-Reply-To: <20150304061026.134125919@linuxfoundation.org> References: <20150304061026.134125919@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: George Spelvin commit 19acc77a36970958a4a0e4daeb2c8cb2aab0ffd4 upstream. There was a bad typo in commit 43759d4f429c ("random: use an improved fast_mix() function") and I didn't notice because it "looked right", so I saw what I expected to see when I reviewed it. Only months later did I look and notice it's not the Threefish-inspired mix function that I had designed and optimized. Mea Culpa. Each input bit still has a chance to affect each output bit, and the fast pool is spilled *long* before it fills, so it's not a total disaster, but it's definitely not the intended great improvement. I'm still working on finding better rotation constants. These are good enough, but since it's unrolled twice, it's possible to get better mixing for free by using eight different constants rather than repeating the same four. Signed-off-by: George Spelvin Cc: Theodore Ts'o Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -569,19 +569,19 @@ static void fast_mix(struct fast_pool *f __u32 c = f->pool[2], d = f->pool[3]; a += b; c += d; - b = rol32(a, 6); d = rol32(c, 27); + b = rol32(b, 6); d = rol32(d, 27); d ^= a; b ^= c; a += b; c += d; - b = rol32(a, 16); d = rol32(c, 14); + b = rol32(b, 16); d = rol32(d, 14); d ^= a; b ^= c; a += b; c += d; - b = rol32(a, 6); d = rol32(c, 27); + b = rol32(b, 6); d = rol32(d, 27); d ^= a; b ^= c; a += b; c += d; - b = rol32(a, 16); d = rol32(c, 14); + b = rol32(b, 16); d = rol32(d, 14); d ^= a; b ^= c; f->pool[0] = a; f->pool[1] = b;