From 19acc77a36970958a4a0e4daeb2c8cb2aab0ffd4 Mon Sep 17 00:00:00 2001 From: George Spelvin Date: Sat, 7 Feb 2015 00:32:06 -0500 Subject: [PATCH] random: Fix fast_mix() function 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 Cc: stable@vger.kernel.org # v3.16+ Signed-off-by: Linus Torvalds --- drivers/char/random.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 04645c09fe5e..9cd6968e2f92 100644 --- 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;